Power tool safety mechanisms

ABSTRACT

A sensing mechanism ( 12 ) for detecting user contact with an active portion ( 26 ) of the power tool ( 10 ) is provided. In addition, a safety mechanism ( 14 ) for preventing prolonged user contact with the active portion ( 26 ) of a power tool ( 10 ) is provided. The safety mechanism ( 14 ) is configured to actuate upon receipt of a signal from the sensing mechanism ( 12 ). According to a first aspect, the safety mechanism ( 14 ) is arranged to rapidly displace the active portion ( 26 ) away from a user extremity. Alternatively, according to a second aspect, the safety mechanism ( 14 ) is arranged to rapidly urge an extremity of the user away from the active portion ( 26 ) of the power tool ( 10 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/441,057, filed Apr. 6, 2012, now issued U.S. Pat. No.8,408,107 which is a continuation application of U.S. patent applicationSer. No. 12/889,855 filed Sep. 24, 2010, now issued U.S. Pat. No.8,186,256 which is a divisional of U.S. patent application Ser. No.11/901,296 filed Sep. 14, 2007, now issued U.S. Pat. No. 7,827,889 whichis a divisional application of U.S. patent application Ser. No.10/753,845 filed Jan. 8, 2004, now issued U.S. Pat. No. 7,373,863 whichis a continuation of International Application No. PCT/US02/21790 filedJul. 11, 2002. PCT/US02/21790 claims benefit of US ProvisionalApplication No. 60/304,614 filed Jul. 11, 2001; US ProvisionalApplication No. 60/309,352 filed Aug. 1, 2001; US ProvisionalApplication No. 60/323,511 filed Sep. 19, 2001; US ProvisionalApplication No. 60/340,191 filed Dec. 14, 2001 and US ProvisionalApplication No. 60/340,612 filed Dec. 14, 2001. The disclosures of theabove applications are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates generally to a safety system for a powertool and, more particularly to various improved safety systems for awoodworking power tool that prevents or reduces potentially injuriouscontact between an active portion of the power tool and a portion of theoperators body.

BACKGROUND OF THE INVENTION

The advent of modern power tools has allowed many material removal andmaterial forming processes that were typically performed by hand to beperformed with greater efficiency, greater precision and typically at alower cost. The modern power tool is typically comprised of three mainsystems, the power system, the tool system and a safety system. Thepower system transfers a first energy type to a second energy type thatthe tool system is able to use. The tool system performs the materialremoval or material forming processes using the energy from the powersystem. Lastly, the safety system prevents dangerous conditions betweenthe tool system and the operator of the power tool.

Many devices utilize power systems to convert an energy source into auseable form. In modern power tools, the power systems typically converteither hydrocarbon based fuels or electrical energy into mechanicalenergy. Hydrocarbon fuel power systems are normally on such devices aschain saws and trimmers; whereas electrical power systems are found onsuch devices as drills and table saws.

In many instances, the tool system of a power tool resembles the handtool that was originally utilized to perform wood working operations.For example, a hand drill and a power drill both utilize a drill bit toremove material in a circular shape from a workpiece. In otherinstances, modern power tools utilize tool systems that are unique. Forexample, a circular saw utilizes a circular shaped saw blade having aplurality of teeth disposed around the circumference of the blade. Whilethe teeth of the circular saw blade are similar to the ones formed on ahand saw, the circular configuration on the blade facilitates rotationalmotion of the blade as it engages a workpiece.

Since many of the safety systems set forth herein are described inrelation to either a table saw or a miter saw, each of these power toolsare further described below. A typical table saw generally includes abase that supports a generally flat table top having a longitudinallyextending throat slot or opening through which a saw blade or othercutting tool protrudes above the table for engaging a workpiece. A motoris mounted beneath the table top, and the cutting tool, typically acircular saw blade, is mounted for rotation to the output shaft of themotor. The saw blade is positioned to effect cutting of the workpiece asit is moved longitudinally along the table. The saw blade can be loweredor raised with respect to the table top to accommodate workpieces ofvarying thicknesses as well as adjusted to various angular orientationsrelative to the plane of the table top in order to cut bevels or othersuch angular cuts on the workpiece.

Additionally, a typical miter saw generally includes a base memberhaving a slot formed therethrough for receiving a saw blade and apivotal support arm coupled to the base member. A saw is mounted to thedistal end of the support arm. When the arm is lowered, the saw bladeengages the workpiece, thereby cutting the workpiece. Additionally, themiter saw may include a mechanism for rotating the support arm around az-axis (upward) relative to the base member for performing angledcutting operations.

Various safety systems have been developed to minimize the risk ofinjury during the operation of such power tools. Exemplary power toolsafety systems may include guard mechanisms and operator detectionsystems. A guard physically prevents the operator from making physicalcontact with the active portions of the tool, such as belts, shafts,blades, etc. However, some power tools preclude the use of a guard thatwould effectively prevent the operator from making contact with theactive portion of the tool. In these instances, operator detectionsystems have been developed to prevent and/or reduce injurious contactbetween the operator and the active portion of the power tool.

A conventional operator detection system for a power tool is generallycomprised of three primary subsystems: a detection subsystem, a controlsubsystem and a reaction subsystem. The detection subsystem or sensingmechanism tracks the proximity of the operator in relation to the activeportion of the power tool. The control subsystem determines theappropriate response to input received from the detection subsystem.Lastly, the reaction system or safety mechanism may initiate aprotective operation, if applicable, that prevents and/or reducespotentially injurious contact between the operator and the activeportion of the power tool. Each of these subsystems are furtherdescribed below.

Detection subsystems operatively determine the location of theoperator's body to the active portion of the power tool. Three knowntypes of detection means are currently employed. First, fixed detectionsubsystems utilize various sensing techniques to determine if aparticular portion of an operator's body is located in a certainposition proximate to the power. For example, a trigger mechanism may belocated on the handle portion of a miter saw. The trigger mechanismensures that the power tool is only operated when the operator's hand isgrasping the handle. If the operator's hand does not engage the triggermechanism, the power tool will not operate, thereby preventing injury tothe operator of power tool. If the trigger is disengaged when the powertool is operating, the trigger mechanism may cut power to the activeportion of the tool.

Second, proximate detection subsystems utilize, various sensingtechniques to determine the proximity of the operator to the activeportion of the power tool. In one known approach, an electrical signalis transmitted through the active portion of the power tool. A receiveris coupled to the operator's body to receive the signal. When the activeportion of the power tool is brought in close proximity to the receiver,the received signal is increased. As the intensity of the receivedsignal increases, the control system determines if the signal intensityexceeds some predetermined threshold level. If so, the control subsystemmay initiate some protective operation to prevent and/or reduce operatorinjury.

Third, contact detection subsystems generally employ various capacitivesensing techniques to determine when the operator physically touches theactive portion of the power tool. In one known approach, an electricalsignal is transmitted from a transmitter to a receiver, where thetransmitter is capacitively coupled via the active portion of the toolto the receiver. When the operator touches the active portion, there isa sudden decrease in the signal level detected at the receiver.Accordingly, if the sensed signal level drops below some predeterminedthreshold level, the control subsystem may initiate some protectiveoperation to prevent and/or reduce operator injury.

Control subsystems determine an appropriate response to input receivedfrom the detection subsystem. When the control system determines thatthe operator's body is in dangerous proximity to the active portion ofthe power tool, it may initiate some protective operation to preventand/or reduce operator injury.

The control subsystem may then interact, if applicable, with thereaction subsystem to carry out a protective operation that preventsand/or reduces potentially injurious contact between the operator andthe active portion of the power tool. The reaction system may preventand/or reduce the potential of operator injury in one of a variety ofways. For example, a braking mechanism may be employed to slow or stopmovement of the active portion of the tool. Alternatively, an activeretraction mechanisms may operatively moves the active portion of thetool away from of the operator's body, thereby prevent injuriouscontact.

The present application sets forth numerous improved safety mechanismsfor preventing and/or reducing potentially injurious contact between anoperator and active portion of a power tool. At least one known safetysystem for power tools is set forth in International Publication No. WO01/26064 which is incorporated by reference herein. It is to beunderstood that the safety mechanisms set forth below may be integratedwith this exemplary safety system and/or other known power tool safetysystems. For a more complete understanding of the present invention, itsobjects and advantages, reference may be had to the followingspecification and to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the sensing mechanism and safety mechanismconfiguration of the present invention;

FIG. 2 is view of a sensing mechanism according to a first embodiment ofthe present invention;

FIG. 3 is a perspective view of a sensing mechanism employed in anexemplary miter saw according to a second embodiment of the presentinvention;

FIG. 4 is a front view of the sensing mechanism of FIG. 3 shownaccording to an alternative embodiment;

FIG. 5 is a perspective view of a sensing mechanism employed in anexemplary miter saw according to a third embodiment of the presentinvention;

FIG. 6 is a diagram of an exemplary table saw which may employ a sensingmechanism according to a fourth embodiment of the present invention;

FIG. 7 is a block diagram of a preferred embodiment of the sensingmechanism of FIG. 6;

FIG. 8 is a graph illustrating a parasitic load making contact with ablade of the table saw of FIG. 6;

FIG. 9 is a graph illustrating three exemplary impedance loadingconditions on the blade of the table saw of FIG. 6;

FIG. 10 is a graph illustrating the three exemplary impedance loadingconditions according to FIG. 9 having added constant parasitic load;

FIG. 11 is a graph illustrating the detected signal level in relation tovarying parasitic loads which may be associated with the operation ofthe table saw of FIG. 6;

FIG. 12 is a graph illustrating the detected signal level of FIG. 11including an ideal curve and the basis for the adjustable thresholdvalue;

FIG. 13 is a graph of the drive voltage of the transmitter in relationto the voltage detected at the receiver for each of the operatingconditions of FIG. 12;

FIG. 14 is a schematic of an exemplary circuit used to derive adynamically adjustable threshold value in accordance with the presentinvention;

FIG. 15 illustrates a known capacitive sensing system;

FIG. 16 illustrates a block diagram of a sensing mechanism according toa fifth embodiment of the present invention;

FIG. 17 is a signal representation of the sensing mechanism of FIG. 16having a signal amplitude near zero;

FIG. 18 is a signal representation of the sensing mechanism of FIG. 17shown with an operator's hand touching a handle of the power tool;

FIG. 19 is a graph of an exemplary sinusoidal voltage employed to reducethe amount of EMI radiation emitted from the capacitive sensing systemof FIG. 16;

FIG. 20 is a perspective view of a sensing mechanism according to asixth embodiment of the present invention;

FIG. 21 is a cutaway view of a sensing mechanism according to a seventhembodiment of the present invention;

FIG. 22 is a cutaway view of a sensing mechanism according to a eighthembodiment of the present invention;

FIG. 23 is a perspective view of a sensing mechanism according to aninth embodiment of the present invention;

FIG. 23 b is a perspective view of a sensing mechanism according to aseventh embodiment of the present invention;

FIG. 24 is a side view of a safety mechanism according to a firstembodiment of the present invention;

FIG. 25 is a side view of a safety mechanism according to a secondembodiment of the present invention;

FIG. 26 a is a side view of a safety mechanism according to a thirdembodiment of the present invention shown prior to actuation;

FIG. 26 b is a side view of the safety mechanism of FIG. 26 a shownafter actuation;

FIG. 27 is a perspective view of a safety mechanism according to afourth embodiment of the present invention;

FIG. 28 is a cutaway view of the safety mechanism of FIG. 27 shown priorto actuation;

FIG. 29 is a cutaway view of the safety mechanism of FIG. 27 shownsubsequent to actuation;

FIG. 30 is a side view of a safety mechanism according to a fifthembodiment of the present invention shown prior to actuation;

FIG. 31 is a side view of a safety mechanism of FIG. 30 shown subsequentto actuation;

FIG. 32 is a cutaway view of the safety mechanism of FIG. 30 taken alongline 32-32 of FIG. 30.

FIG. 33 is a side view of a safety mechanism according to a sixthembodiment of the present invention prior to activation;

FIG. 34 is a side view of the safety mechanism of FIG. 33 shownsubsequent to activation;

FIG. 35 is a side view of a safety mechanism according to a seventhembodiment of the present invention shown prior to activation;

FIG. 36 is a side view of the safety mechanism of FIG. 35 shownsubsequent to activation;

FIG. 37 is a side view of a safety mechanism according to a eighthembodiment of the present invention shown prior to activation;

FIG. 38 is a side view of the safety mechanism of FIG. 37 shownsubsequent to activation;

FIG. 39 a is a side view of a safety mechanism according to a ninthembodiment of the present invention shown immediately after activation;

FIG. 39 b is a side view of the safety mechanism of FIG. 39 a shownafter engagement with a user;

FIG. 40 a is a side view of a safety mechanism according to a tenthembodiment of the present invention shown prior to activation;

FIG. 40 b is a side view of the safety mechanism of FIG. 40 a shownafter activation;

FIG. 41 is a side view of a safety mechanism according to a eleventhembodiment of the present invention shown prior to activation;

FIG. 42 is a side view of the safety mechanism of FIG. 41 shown afteractivation;

FIG. 43 is a side view of a safety mechanism according to a twelfthembodiment of the present invention Shown prior to activation;

FIG. 44 is a side view of the safety mechanism of FIG. 43 shown afteractivation;

FIG. 45 is a side view of a safety mechanism according to a thirteenthembodiment of the present invention shown prior to activation;

FIG. 46 is a side view of the safety mechanism of FIG. 45 shown afteractivation;

FIG. 47 a is a side view of a safety mechanism according to a fourteenthembodiment of the present invention shown prior to activation;

FIG. 47 b is a side view of the safety mechanism of FIG. 47 a shownafter activation;

FIG. 47 c is a side view of a safety mechanism according to a fifteenthembodiment of the present invention shown prior to activation;

FIG. 47 d is a perspective view of the leaf spring stop of the safetymechanism of FIG. 47 c;

FIG. 48 is a perspective view of a safety mechanism according to asixteenth embodiment of the present invention;

FIG. 49 is a cutaway view of the safety mechanism of FIG. 48 shown priorto actuation;

FIG. 50 is a cutaway view of the safety mechanism of FIG. 48 shownsubsequent to actuation;

FIG. 51 is a side view of a safety mechanism according to a seventeenthembodiment of the present invention shown prior to activation;

FIG. 52 is a side view of the safety mechanism of FIG. 51 shown afteractivation;

FIG. 53 is a side view of a safety mechanism according to a eighteenthembodiment of the present invention shown prior to activation;

FIG. 54 is a side view of the safety mechanism of FIG. 53 shown afteractivation;

FIG. 55 is a side view of a safety mechanism according to a nineteenthembodiment of the present invention shown prior to activation;

FIG. 56 is a side view of a safety mechanism according to a twentiethembodiment of the present invention shown prior to activation;

FIG. 57 is a perspective view of a safety mechanism according to atwenty-first embodiment of the present invention;

FIG. 58 is a side view of the safety mechanism of FIG. 57 shown prior toactivation;

FIG. 59 a is a side view of a safety mechanism according to atwenty-second embodiment of the present invention shown prior toactivation;

FIG. 59 b is a side view of the safety mechanism of FIG. 59 a shownafter activation;

FIG. 60 a is a side view of a safety mechanism according to atwenty-third embodiment of the present invention shown prior toactivation;

FIG. 60 b is a side view of the safety mechanism of FIG. 60 a shownafter activation;

FIG. 61 a is a side view of a safety mechanism according to atwenty-forth embodiment of the present invention shown prior toactivation;

FIG. 61 b is a side view of the safety mechanism of FIG. 61 a shownafter activation;

FIG. 62 a is a side view of a safety mechanism according to atwenty-fifth embodiment of the present invention shown prior toactivation;

FIG. 62 b is a side view of the safety mechanism of FIG. 62 a shownafter activation;

FIG. 63 a is a view of a safety mechanism according to a twenty-sixthembodiment of the present invention;

FIG. 63 b is a side view of the friction stopping device of FIG. 63 a;

FIG. 63 c is a view of a safety mechanism according to a twenty-seventhembodiment of the present invention;

FIG. 64 a is a side view of a safety mechanism according to atwenty-eighth embodiment of the present invention shown prior toactivation;

FIG. 64 b is a side view of the safety mechanism of FIG. 64 a shownafter activation;

FIG. 64 c is a side view of a safety mechanism according to atwenty-ninth embodiment of the present invention shown prior toactivation;

FIG. 64 d is a side view of the safety mechanism of FIG. 64 c shownafter activation;

FIG. 64 e is a side view of a safety mechanism according to a thirtiethembodiment of the present invention shown prior to activation;

FIG. 64 f is a side view of the safety mechanism of FIG. 64 e shownafter activation;

FIG. 64 g is a side view of a safety mechanism according to athirty-first embodiment of the present invention shown prior toactivation;

FIG. 64 h is a side view of the safety mechanism of FIG. 64 g shownafter activation;

FIG. 64 i is a side view of a safety mechanism according to athirty-second embodiment of the present invention shown prior toactivation;

FIG. 64 j is a side view of the safety mechanism of FIG. 64 i shownafter activation;

FIG. 65 a is a view of a safety mechanism according to a thirty-thirdembodiment of the present invention;

FIG. 65 b is a view of the safety mechanism of FIG. 65 a shown removedfrom the exemplary miter saw;

FIG. 66 a is a view of a safety mechanism according to a thirty-fourthembodiment of the present invention;

FIG. 66 b is a sectional view of the safety mechanism of FIG. 66 a takenabout line 66 b-66 b of FIG. 66 a shown prior to activation;

FIG. 66 c is a sectional view of the safety mechanism of FIG. 66 b shownafter activation;

FIG. 67 a is a top view of a safety mechanism according to athirty-fifth embodiment of the present invention;

FIG. 67 b is a side view of the safety mechanism of FIG. 67 a;

FIG. 68 a is a side view of a safety mechanism according to athirty-sixth embodiment of the present invention shown prior toactivation;

FIG. 68 b is a side view of the safety mechanism of FIG. 68 a shownafter activation;

FIG. 69 is a side view of a safety mechanism according to athirty-seventh embodiment of the present invention;

FIG. 70 is a side view of a safety mechanism according to athirty-eighth embodiment of the present invention;

FIG. 71 is a sectional view of a protection mechanism according to afirst embodiment of the present invention;

FIG. 72 is a sectional view of a protection mechanism according to asecond embodiment of the present invention;

FIG. 73 is a sectional view of a protection mechanism according to athird embodiment of the present invention;

FIG. 74 a is a side view of a safety mechanism according to athirty-ninth embodiment of the present invention shown prior toactivation;

FIG. 74 b is a side view of the safety mechanism of FIG. 74 a shownafter activation;

FIG. 75 a is a side view of a safety mechanism according to a fortiethembodiment of the present invention shown prior to activation;

FIG. 75 b is a side view of the safety mechanism of FIG. 75 a shownafter activation;

FIG. 76 a is a side view of a safety mechanism according to aforty-first embodiment of the present invention shown prior toactivation;

FIG. 76 b is a side view of the safety mechanism of FIG. 76 a shownafter activation;

FIG. 77 a is a side view of a safety mechanism according to aforty-second embodiment of the present invention shown prior toactivation;

FIG. 77 b is a side view of the safety mechanism of FIG. 77 a shownafter activation;

FIG. 78 a is a perspective view of a safety mechanism according to aforty-third embodiment of the present invention;

FIG. 78 b is a side view of the safety mechanism of FIG. 78 a shownadjusted to accommodate a small saw blade;

FIG. 78 c is a side view of the safety mechanism of FIG. 78 a shownadjusted to accommodate a large saw blade;

FIG. 79 is a perspective view of a safety mechanism according to aforty-fourth embodiment of the present invention;

FIG. 80 is a perspective view of a safety mechanism according to aforty-fifth embodiment of the present invention;

FIG. 81 is a perspective view of a safety mechanism according to aforty-sixth embodiment of the present invention;

FIG. 82 is a perspective view of a safety mechanism according to aforty-seventh embodiment of the present invention;

FIG. 83 is a perspective view of a safety mechanism according to aforty-eighth embodiment of the present invention;

FIG. 84 is a perspective view of a safety mechanism according to aforty-ninth embodiment of the present invention;

FIG. 85 is a perspective view of a safety mechanism according to afiftieth embodiment of the present invention;

FIG. 86 is a perspective view of a safety mechanism according to afifty-first embodiment of the present invention;

FIG. 87 is a perspective view of a safety mechanism according to afifty-second embodiment of the present invention;

FIG. 88 is a perspective view of a safety mechanism of FIG. 87 employinga bumper stop;

FIG. 89 is a perspective view of a safety mechanism according to afifty-third embodiment of the present invention;

FIG. 90 is a perspective view of a safety mechanism according to afifty-third embodiment of the present invention;

FIG. 91 is a side view of a safety mechanism according to a fifty-fourthembodiment of the present invention;

FIG. 92 is a side view of the braking system of the safety mechanism ofFIG. 91;

FIG. 93 is a partial top view of a braking system constructed inaccordance to a second embodiment of FIG. 91;

FIG. 94 is a partial top view of a braking system constructed inaccordance to a third embodiment of FIG. 91;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, the plurality of safety systems 20 set forthin the following embodiments generally include three main subsystems,namely a power tool 10, sensing mechanism 12 and safety mechanism 14.Each subsystem disclosed herein includes a variety of configurationsemploying several components for each subsystem. As will be furtherdescribed below, these subsystems may be used in conjunction or invarious combinations to achieve specific safety advantages. For clarity,each power tool 10, sensing mechanism 12 and safety mechanism 14described herein will include a unique suffix such as a, b, c etc.

It will be understood that the various safety mechanisms 14 set forthherein may be integrated with this or other well known power tool safetysystems. Moreover, while a preferred embodiment of a safety mechanism 14may be shown in conjunction with a particular power tool 10, it isenvisioned that the various safety mechanisms may be adapted for usewith other types of power tools.

Safety Guard Switch

As shown generally in FIG. 2, power tool 10 a includes a miter sawhaving a circumferential guard 18. Although the following description isdirected to a miter saw, it will be appreciated that the safety devicedescribed herein may also be used in conjunction with other power toolsemploying a safety guard. Miter saw 10 a has a circular saw blade 26which is shielded by the guard 18. The guard 18 is pivotally attached tomiter saw 10 a, and also has a pivot arm assembly 28 linked between themiter saw arm 32 and the guard 18 to help ensure proper articulation ofthe guard 18 throughout the range of movement of the miter saw 10 a.Prior to or during a cutting procedure on workpiece 30, it may benecessary for the operator to change the saw blade 26. To gainsufficient access to the saw blade 26, the user typically removes thesafety guard 18.

According to a preferred embodiment, sensing mechanism 12 a includes aswitch or sensing device 22 disposed on the safety guard 18 to detectthe position of the guard 18. When the guard 18 is not installed, orinstalled improperly, the sensing device 22 precludes operation of theelectric motor (not specifically shown) thereby disabling blade 26.Likewise, if the guard 18 is positioned in the proper orientation, theswitch 22 enables operation of the electric motor and consequentlyrotation of saw blade 26. Switch 22 preferably includes a pair ofelectrical contacts, one positioned on guard 18 and one positioned on aguard mounting hub 24 disposed on pivot arm 32. In this regard, whenguard 18 is properly mounted on hub 24, the electrical contacts form acomplete electrical loop allowing switch 22 to permit operation of theelectric motor. It will be appreciated that switch 22 may comprisealternate sensing mechanisms which adequately identify a properorientation of guard 18.

Dual Safety Switch System

With reference to FIG. 3 a power tool 10 b employing a sensing mechanism12 b according to a second embodiment of the present invention is shown.The exemplary power tool embodied herein is a miter saw, however it isappreciated that the safety system of the present invention may beadapted for use with a variety of power tools. Miter saw 10 b generallycomprises a base portion 40, an angularly movable table assembly 42, andan angularly movable housing assembly 44 having a pivotally attacheddrive assembly 46. The drive assembly 46 is generally comprised of anelectrical motor 48 drivingly coupled by way of an extension arm 50 tosaw blade 52. Positioned at the distal end of the arm 50 is saw blade 52and a handle portion 54 for controlling articulation of the saw blade 52to engage a workpiece. The base portion 40 of the miter saw 10 bincludes a fence portion 56 for positioning a workpiece relative to thesaw blade 52. The electrical motor 48 of the power tool 10 b isactivated by a trigger mechanism 58 located in the handle portion 54 ofthe arm 50

In operation, an operator positions a workpiece along the fence 56 ofthe base portion 40 and activates the trigger mechanism 58 to operatethe saw blade 52. During operation, the operator articulates the sawblade 52 into engagement with the workpiece to remove a portion of theworkpiece. According to the present invention, a sensing mechanism 12 boperatively detects the location of the operator's first and second handduring operation of the power tool 10 b to ensure that the operator'sfirst and second hands are away from the saw blade 52 of the power tool10 b to reduce the chance of injurious contact between a portion of theoperator's body and the active portion of the power tool 10 b.

The sensing mechanism 12 b generally includes a first switch or sensor66 positioned in the handle portion 54 of the power tool 10 b operableto detect an operator's first hand, a second switch or sensor 68positioned in a second location operable to detect an operator's secondhand and a controller coupled to the first and second sensors operableto prevent operation of the power tool 10 b when either the first or thesecond sensors do not detect an operator's hand. The sensing mechanism12 b reduces/prevents potentially injurious situations between theoperator's hands and the active portion of the power tool 10 b byensuring that the operator's hands are located away from the saw blade52 during operation of the power tool 10 b.

The first sensor 66 of the sensing mechanism 12 b is located in thehandle portion 54 of the power tool 10 b. The first sensor 66 ensuresthat the operator's first hand is placed on the handle 54. As shown inFIG. 3, the first sensor 66 is located along an upper portion of thehandle 54. The first sensor is preferably oriented to allow the operatorto easily activate the first sensor 66 during normal operation of thepower saw 10 b. It is appreciated that first sensor 66 may be located atother locations on handle 54.

The second sensor 68 of the sensing mechanism 12 b is positioned toprevent injurious contact between the operator's second hand and theactive portion of the power tool 10 b. As shown in FIG. 3, the secondsensor 68 is located along the left side of the fence portion 68 of thepower tool 10 b. In this location, the second hand of the operator willbe positioned away from the active portion 60 of the power tool 10 b. Itis appreciated that the second sensor 68 may be located at variouspositions on the power tool 10 b to ensure that the second hand of theoperator is safely away from the saw blade 52 of the power tool 10 b.For example, in an alternate embodiment shown in FIG. 4, power tool 10b′ includes a second sensor 68′ located along the front of the baseportion 42 of the miter saw to ensure that the operator's second hand issafely away from the active portion of the power tool 10 b′. Thisconfiguration allows a user to depress sensor 68 with a thumb whilemanipulating the workpiece with fingers safely away from active portion60 of power tool 10 b′.

Returning to FIG. 3, it is contemplated that a plurality of secondsensor's may be used with the sensing mechanism 12 b of the presentinvention to allow for alternative configurations of the operator'shands. For example, second sensors may be positioned along the left sideand the right side of the fence 56. In this configuration a left orright handed operator could utilize the safety system of the presentinvention during operation of the power tool 10 b.

The controller (not specifically shown) is coupled to the first andsecond sensors 66, 68 and the electric motor of the power tool 10 b. Thecontroller is operable to allow operation of the power tool 10 b whenthe first and the second sensors 66, 68 detect the first and secondhands of the operator, respectively. If the controller detects that theoperator's hands are in the correct position, the saw blade 52 of thepower tool 10 b is allowed to be operated. The controller of the presentinvention may be any of a variety of controllers, microcomputers orother devices suitable to detect activation of the first and secondsensors 66, 68 and in turn allow operation of the saw blade 52.

The controller is preferably coupled to the first sensor 66 and thesecond sensor 68 in a series type configuration. In the series typeconfiguration the controller includes a single input and single outputconnected to the controller. The first and second sensors 66, 68 areconnected to the single input and single output to form a loop. Thecontroller detects the desired positioning of the operator's hands whenthe first and the second sensors 66, 68 are both activated, allowing acompletion of the circuit from the input to the output. When thecontroller detects that the first and second hands of the operator arein the desired position, the controller allows operation of the powersaw 10 b.

The controller may also be coupled to the first and second sensors 66,68 in a parallel type configuration. In a parallel configuration, eachof the first and the second sensors are coupled to a separate input anda separate output on the controller. The parallel configuration requiresthat the controller determine that both the first and the second sensors66, 68 are activated at the same time to allow operation of the sawblade 52 of the power tool 10 b.

In a preferred embodiment, the first sensor 66 is located in the handleportion 54 of the miter saw 10 b and is activated while the operator isgrasping the handle portion 54 of the miter saw and the second sensor 68is located along the fence 56 of the miter saw 10 b. In operation, theoperator of the miter saw 10 b activates the first switch 66 whilegrasping the handle portion 54 and activates the second switch 68 whileholding a workpiece against the fence portion 56. In this configuration,both the operator's first and second hands are located away from the sawblade 52 of the power tool 10 b. The first and second sensors 66, 68 maybe any of a variety of sensors that detect the presence of an operator'shand. A preferred sensor is a electrical switch sensor that is activatedwhen a portion of the operator's hand depresses a plunger or otherdevice to indicate physical presence of the operator's hand.

Another type of sensor that may be used for the first and the secondsensors are electromagnetic signal sensors. The electromagnetic signalsensor transmits an electrical signal from a transmitter. A receiver,typically adjacent to the transmitter receives the transmittedelectromagnetic signal. The received electromagnetic signal is comparedto a threshold value to determine if the operator's hand is proximal tothe sensor. The electromagnetic signal sensor signals the controller tothe presence of the operator's hand. Some commonly known electromagneticsignal sensors are proximity switches, light curtains or hall effectsensors.

Yet another type of sensor that may be used for the first and secondsensors 66, 68 are electrical capacitance sensors. Electricalcapacitance sensors are typically comprised of a capacitance measuringdevice that determines the electrical capacity around the sensor. Theelectrical capacitance sensor monitors the electrical capacity andcompares it to a threshold value. Generally, when a portion of theoperator's hand comes in close proximity or touches the sensor, theelectrical capacity increases. If the capacitance exceeds a thresholdvalue, the electrical capacitance sensor signals the controller to thepresence of the operator's hand.

During many operations, the operator will utilize one of his/her handsto guide the workpiece relative to the saw blade 60 or restrain theworkpiece relative to the saw blade 60. Therefore, it is desirable tolocate the second switch 68 in a position that the operator normallyutilizes to guide or restrain the workpiece. In a first configuration,the operator's other hand is utilized to restrain a workpiece to theguide fence 56 of the power tool 10 b. The guide fence 56, as describedabove typically extends outward from a first and second side of the sawblade 52 to provide a guide that is relatively perpendicular to the sawblade 52. In this configuration, an operator may hold the workpiece tothe fence 56 by gripping the workpiece with their thumb and back of thefence with their fingers to clamp them together. In this configuration,a second switch 68 could be located along the rear of the fence 56 (asshown in FIG. 3, switch 68 is accessible from the front of fence 56 butmay alternatively be accessible at a location on the rear of fence 56)to allow the fingers of the operator to positively engage the secondswitch 68 when positioned away from the saw blade of the power tool.

Turning to FIG. 4, in a second configuration, a workpiece having arelatively large width is restrained to the table portion 42 of thepower tool 10 b′ by an operator. In this configuration, the fingers ofthe operator are typically used to push downward on the workpiece torestrain it relative to the saw blade causing the thumbs of the operatortypically overhang the front edge of the table portion. In thisconfiguration, a switch is being mounted along the front edge of thetable portion of the miter saw. In this configuration, the operatorwould positively secure the second safety switch 68′ to indicate thathis first and second hands are not located within dangerous proximity ofthe saw blade 52 of the power tool 10 b′.

FIG. 5 shows a sensing mechanism 12 c in the form of a light switch thatprevents a power tool 10C from being operated if a foreign object isnear the saw blade 52. Like reference numerals associated with miter saw10 c are used to denote like components identified in relation to mitersaw 10 b. Sensing mechanism 12 c is composed of at least one lightemitting panel 70 and at least one light receiving panel 72 in operativecommunication. Light emitting panel 70 is preferably positioned ateither the front or rear portion of the saw blade 52 and oriented toemit light along the planar direction of saw blade 52. Light receivingpanel 72 is preferably positioned at the other of the front or rearportion of the saw blade and oriented to receive light emitted along theplanar portion of saw blade 52. If an object prevents light from thelight emitting panel 70 from being received by light receiving panel 72,saw blade 52 is stopped to prevent contact of the blade 52 with aforeign object, namely a human extremity.

Light emitting and light receiving panels 70, 72 are connected to acontroller (not specifically shown) as well as electric motor 48. Whenlight is not received by light receiving panel 72, the controller shutsdown power to electric motor 48.

Capacitive Sensing

1. Variable Limit Setting Based on Parasitic Load

FIG. 6 illustrates an exemplary table saw 10 d, which may employ asensing mechanism 12 d in accordance with the present invention. Thetable saw 10 d generally includes a table portion 102 having a slot 104therethrough for receiving a saw blade 106. The saw blade 106 is indriving engagement with a motor assembly (not shown) as is well known inthe art. To cut a workpiece, the operator 108 guides a workpiece 110into contact with the saw blade 106 as shown in FIG. 6. While thefollowing description is provided with reference to a table saw, it isreadily understood that the sensing mechanism 12 d of the presentinvention is applicable to a variety of power tools and/or woodworkingtools, including (but not limited to) miter saws, radial arm saws,circular saws, band saws, joiners, planers, nailers, drills, etc.

Sensing mechanism 12 d is configured to minimize and/or prevent seriousinjury to the operator of the table saw 10 d as will be more fullydescribed below. Briefly, the sensing mechanism 12 d is operable todetect the proximity of the operator 108 to the saw blade 106. Upondetection of a dangerous condition, the sensing mechanism 12 d willtrigger a protective operation intended to reduce the potential foroperator injury.

FIG. 7 illustrates the sensing mechanism 12 d of the present inventionin the context of the above-described table saw 10 d. The sensingmechanism 12 d is intended to determine if a human operator of the sawhas made contact with an active portion of the saw 10 d. The activeportion should be a conductive object that is inherently dangerous, suchas a saw blade, punch, press, router/drill bit or other mechanicallymoving device. In this case, the active portion of the saw is the sawblade 106.

To determine if the operator has touched the saw blade, an AC signalcoupled through the saw blade 106 is monitored for changes. To do so,the sensing mechanism 12 d includes a transmitter 112 capacitivelycoupled to the electrically isolated saw blade 106 (or arbor shaft)which in turn is capacitively coupled to a receiver 114. Morespecifically, the transmitter 112 is electrically coupled to atransmitting plate 118 disposed adjacent to the saw blade 106. Thetransmitting plate 118 is capacitively coupled to the saw blade 106,such that a charge on the transmitting plate 118 is mirrored to the sawblade 106. Likewise, a receiver plate 120 is capacitively coupled to thesaw blade 106 (or arbor shaft) in a similar manner as the transmitter112, so that this differential charge is also mirrored to the receiverplate 120. The receiver plate 120 is then electrically coupled to areceiver 114. In this way, the receiver 114 is configured to sense theAC signal from the transmitter 112.

When the human 108 touches the saw blade 106, it will cut into theirskin. As the blade 106 touches the moist conductive tissue just beneaththe dry layer of skin cells, the electric charge on the blade 106 willbe shared with the human body 108. The sensed signal level at thereceiver 114 suddenly drops when the human operator comes into contactwith the saw blade 106. The human operator 108 is essentially shortingout the receiver 114. When there is such a rapid change in the detectedsignal intensity, it is assumed that the operator 108 has touched thesaw blade 106.

Referring to FIG. 7, a detection circuit 126 is used to monitor thesignal intensity at the receiver 114. It is envisioned that thedetection circuit 126 may be constructed using well-known analog circuitcomponents or implemented in software embodied in a programmablecontroller. In any event, the detection circuit 126 is operable todetect a sudden drop in the signal intensity and, in response to suchsignal drop, to activate a protective operation such as a safetymechanism 14 disclosed herein which may prevent and/or reduce the riskof injury to the operator 108. For instance, the protective operationmay be a mechanical braking mechanism 130 that is actuated to stop therotation of the saw blade. It is to be understood that other protectiveoperations (e.g., visible or audible alarms) are also within the broaderaspects of the present invention.

Referring now to FIGS. 7 and 8, in order to maintain a measurable signalat the receiver, feedback control may be utilized to control themagnitude of the signal level detected at the receiver 114. Since themagnitude of the sensed signal may be attenuated by various impedancefactors associated with the operation of the saw, the magnitude of thetransmitted signal (also referred to as the drive signal) is adjustedbased on the signal level detected at the receiver 114. Specifically,the detection circuit 126 continually monitors the magnitude of thesensed signal 134 in relation to a reference signal value 136. When themagnitude of the sensed signal 134 is above the reference value 32, themagnitude of the transmitted signal is reduced proportionally. On theother hand, when the magnitude of the sensed signal 134 is below thereference value 32, the magnitude of the transmitted signal isincreased. It is envisioned that feedback control is done at a lowfrequency so as not to interfere with the detection of operator contactwith the saw blade 106 As seen in FIG. 8, a sudden parasitic load makescontact with the blade 106 at time T0 causing signal 134 to drop awayfrom calibration line 136. As FIG. 8 shows, increasing the transmittedoutput magnitude compensates for the drop in signal 134 and eventuallythe signal 134 will match the reference 138. Note that the signal 134did not cross the threshold 138 so the circuit never triggered a safetymechanism.

Referring to FIG. 9, a simulation shows three different impedanceloading conditions on the blade. In Stage 1, the signal 134 iscalibrated to the reference voltage 138. Neglecting feedback andapplying typical wet wood impedance to the blade would produce a drop inthe signal 134 as seen in Stage 2. The third stage of the simulation, isa result of only the human touching the blade without the parasiticload. For simplicity, the signal 134 is not compensated to display thedifferent attenuation levels between human and wood impedance loads. Inthis situation, the system will allow the impedance load in stage 2 butwill trigger in stage 3.

FIG. 10 represents the same simulation but with added constant parasiticload to all three stages. The system was initially allowed to compensatefor the new parasitic load (not shown before stage 1) as a result, stage1 is identical to FIG. 9. Stages 2 and 3, however, act in the samemanner as before but with different attenuation levels. In this case,none of the stages will trigger the safety mechanism. In this situation,the threshold level 138 should have been increased above the Stage 3level but below the Stage 2 level.

Turning now to FIG. 11, to determine the best place for the thresholdlevel, the minimum impedance for stage 2 and the maximum impedance forstage 3 are used across a wide range of nominal parasitic capacitance.The minimum impedance is used for wood in stage 2 to keep the curve 140as low as possible (worst case.) The maximum human impedance is used instage 3 to keep the curve 142 as high as possible (worst case.) Betweenthese two curves is the ideal threshold level. FIG. 11 represents thesecurves plotted against the parasitic capacitance. Clearly; a constantthreshold voltage level would be prone to false trip and miss fire.

To illustrate this point, assume that the threshold voltage is set at8.0 volts in FIG. 4. For stage 1 curve 144 & stage 2 curve 142, thesensing mechanism 12 d properly operates across a wide range ofparasitic capacitive loads. However, when capacitive loads associatedwith the saw exceed 400 pF, the sensing mechanism 12 d may not detectoperator contact with the saw blade 106. In other words, after humancontact, the voltage level for stage 3 curve 142 does not drop below the8.0-volt threshold. Conversely, if the threshold value is set at 8.3volts, the sensing mechanism 12 d would accurately detect operatorcontact with the saw blade 106 when capacitive loads exceed 400 pF, butmay inaccurately initiate protective measures when capacitive loads arebelow 75 pF. Accordingly, the threshold value for the sensing mechanism12 d should vary based on the parasitic capacitance associated with theoperation of the saw.

FIG. 12 illustrates the basis for an exemplary dynamically adjustablethreshold value. The ideal curve 148, which is the basis for theadjustable threshold value, is preferably plotted halfway between stage2 curve 42 and stage 3 curve 40 in order maximize sensitivity of thedetection system and yet minimize occurrence of false triggers.

Since the parasitic capacitance associated with the operation of the sawis not easily determined, it is envisioned that the adjustable thresholdvalue may be derived from another operational parameter of the saw. Foreach of the operating conditions described above, FIG. 13 plots thedrive voltage of the transmitter 112 in relation to the voltage detectedat the receiver 114. One skilled in the art will readily recognize thatthe curve for each different operating condition correlates to thecorresponding curves in FIGS. 8-12. In other words, the parasiticcapacitance associated with the operation of the saw correlates to thedrive voltage of the transmitter. Therefore, the desired threshold valuemay also be correlated to the drive voltage of the transmitter 112.

FIG. 14 illustrates an exemplary analog circuit 150 that may be used toderive the adjustable threshold value in accordance with the drivevoltage of the present invention. While one exemplary embodiment hasbeen provided with specific components having specific values andarranged in a specific configuration, it will be appreciated that thisfunction may be constructed with many different configurations,components, and/or values as necessary or desired for a particularapplication. The above configurations, components and values arepresented only to describe one particular embodiment that has proveneffective and should be viewed as illustrating, rather than limiting,the present invention.

2. Handle Mounted Transmitter/Receiver Pair for Proximity Sensing

Contrary to the first embodiment, the following is a description of analternate sensing mechanism 12 e hereinafter referred to as proximitysensing. Whereas the previous circuit triggered on the lack of a signal,the following will trigger on the presence of a signal. FIG. 15illustrates a known capacitive sensing system 160. In system 160 atransmitter 162 is connected to the handle or trigger portion of thetool 164 and broadcasts a signal. The signal is capacitively coupled tothe operator 170. The receiver 172 is connected to the active portion ofthe tool 174. When the operator 170 is holding the tool correctly, thesignal is transmitted through the person 170 to the receiver 172. As theoperator 170 approaches the active portion of the tool 174, the signalintensity on the receiver 172 increases until some predetermined levelis reached. At that point a predetermined action is performed, such asbraking of motor/blade or other safety mechanism 14 disclosed herein toprevent and/or reduce bodily injury.

The improvement of the present invention, lies in the fact that if theoperator 170 is touching a grounded object (table surface 102 of FIG. 6)the signal path is essentially shorted out. With the operator 170touching both the transmitter 162 and the grounded object, the signalintensity in the operator 170 is very low. Even when accidental operatorcontact with the active portion of the tool 174 has occurred, the signalamplitude picked up by the receiver 172 might not be high enough totrigger an employed safety mechanism 14.

To correct this situation, a second receiver is needed. Referring toFIG. 16, sensing mechanism 12 e is shown. The addition of secondreceiver 180 and feedback control circuit 182 provide a constant signallevel in the operator 170 regardless of operator grounding. The receiver180 is mounted in relation to the transmitter 162 such that no couplingexists until the user 170 is grasping the handle or trigger portion ofthe tool. Only then, does the receiver 180 receive a signal. To thoseskilled in the art of antenna theory, it is easily recognized that thereceived signal amplitude will be proportional to the signal amplitudein the operator's body. FIG. 17 visually describes this system.Transmitter 200 and receiver 202 are located just inside the handle 204of the tool. A ground plane 206 is placed to cancel any signal thatwould naturally propagate from transmitter 200 to receiver 202. As shownby the electric field lines 208, the receiver signal amplitude is nearzero. In FIG. 18, the operator's hand 210 is wrapped around handle 204.The electric field lines picked up by the operator 170 are continuousaround the handle 204 because the human body is conductive. The fieldlines 206 now can reach the receiver 202 and provide signal amplitudeproportional to the amplitude in the operator 170.

The feedback control 182 regulates the transmitted signal amplitude. Ifthe signal on the receiver 180 is greater than some predeterminedreference level, it is assumed that the level in the operator 170 isgreater than the desired amount as well. The feedback control 182 thendecreases the amplitude of the transmitted signal until the signalstrength on receiver 180 reaches the predetermined level. In contrast,if the operator 170 holding the tool suddenly touches a grounded object,the signal strength in the operator 170 would drop. Accordingly, thesignal on the receiver 180 would also drop. The feedback control 182recognizes this and compensates by increasing the transmitter amplitude.By keeping the signal in the operator 170 constant, the signal receivedby the active portion of the tool 174 is proportional only to thedistance from the operator 170 to the active portion of the tool 174.

It is additionally possible to change the feedback control 182. Insteadof modifying the transmitted amplitude, the feedback control couldmodify the threshold value. When the signal on the receiver 180 isdropping, the circuit would have the same sensitivity if the thresholdof original receiver 172 were lowered as well.

3. Lowered EMI on Capacitive Sensing

FIG. 19 illustrates a method of reducing the amount of electromagneticinterference (EMI) radiation that is emitted from a capacitive sensingsystem. Outputting a sinusoidal voltage 184 on a piece of metal anddetecting the received signal is the basis for capacitive sensing. Thegreater the frequency and the greater the amplitude, the more sensitivethe system is. Unfortunately, any conductive object of changing voltageproduces radiated EMI. Global compliance standards limit the amount ofboth conducted and radiated fields from most electronic/electricaldevices and machines. By varying the frequency of oscillation, there isnot a single frequency radiated. Instead, there will be a band offrequencies with an elevated radiated emission. Since the energyradiated will be the same in a single frequency versus a band offrequencies, the measured amplitude of the band will be much lower thanthe amplitude of the single frequency. The lower the amplitude, the morelikely the signal is below the required limits.

Additionally, as is generally known any signal such as the AC signal ofthe sensing mechanism 12 d when coupled to an electrically conductivebody such as a saw blade of the sensing mechanism 12 d, emits radiatedelectromagnetic interference. The frequency of the radiatedelectromagnetic interference is directly related to the frequency of theAC signal that is transmitted to the active portion of the power tool.Also, the magnitude of the radiated electromagnetic interference isrelated to the magnitude AC signal that is transmitted to the activeportion of the power tool. Additionally, the capacitive sensing systemof the present invention generally increases in sensitivity as theamplitude and the frequency of the AC signal that is transmitted fromthe transmitter to the saw blade is increased. The electrical signalfield strength of radiated emissions in devices not intended to beradiation devices is limited by the Code of Federal Regulations for theprotection of operators and electromagnetic compatibility with otherelectronic devices. The Code of Federal Regulations 47 C.F.R. 15.109limits the amount of radiated emission based on the band of thefrequency of emission. Therefore, it is desirable to vary the frequencyof AC signal from the transmitter to allow a signal having large fieldstrength to be dispersed over multiple different emission bands. Thevariation of the frequency allows the relatively high amplitude of theAC signal to be dispersed over a broad band of frequencies to reduce thepeak radiated electromagnetic interference in a single frequency. Thebroad band of frequencies allows the capacitive sensing system of thepresent invention to operate at desired radiated EMI levels to conformto reduce interference with other electronic devices and provide saferoperation by the operator.

The frequency of the AC signal is preferably varied by a ramp shapedfunction wherein the frequency is alternated between a minimum frequencyand a maximum frequency in a linear pattern. It is also appreciated thatthe frequency of the AC signal may be varied by other patterns such assinusoidal, step, random or others to select and disperse the level ofthe radiated EMI.

Alternative Sensing

FIG. 20 illustrates a safety system employing a sensing mechanism 12 faccording to an additional embodiment of the present invention. Thesensing mechanism 12 f detects when a portion of the operator's body isin dangerous proximity to the active portion of the power tool toprevent/reduce injuries. If a dangerous condition is detected, acontroller operates a protective measure such as a safety mechanism 14disclosed herein with respect to the active portion of the power tool.The sensing mechanisms 12 described according to this embodiment areshown operatively associated with a power table saw and a miter saw. Itwill be appreciated however, that the sensing system may also beemployed to other tools such as but not limited to planers, jointers ordrills.

FIG. 20 illustrates sensing mechanism 12 f including generator 202operatively associated with a miter saw 10 f, for detecting when a humanextremity is in close proximity to a rotating saw blade 204. Generator202 is an electrostatic charge generator attached to the rotating sawblade 204. If a human extremity or other object having a capacitance andcharge that is relatively lower than the charge on the saw blade 204, anelectrostatic charge in the form of a spark will act on the humanextremity. In a preferred embodiment, the generator 202 includes a VanDe Graff generator to generate the electrostatic charge however, it isappreciated that other electrostatic charge generators may be employed.The transfer of the spark to the operator's hand will alert the operatorthat a portion of his body is too close to the saw blade 204.

FIG. 21 shows a sensing mechanism 12 g including transmitter or depthsensor 214 that senses if a human extremity is in close proximity to arotating saw blade 208. Transmitter 214 is shown operatively associatedwith table saw 10 g and is operable to monitor the depth (thickness) ofthe workpiece 218 that is being fed into saw blade 208. In most cuttingoperations, the thickness of the workpiece 218 that is being cut isrelatively consistent. In this way, if depth sensor 214 detects a suddenchange in the depth (thickness) of the workpiece 218, a switch 216 isactivated to stop saw blade 208 as a precautionary measure to preventcontact of human extremities with saw blade 208. It is appreciated thatswitch 216 may also comprise any of the safety mechanisms 14 disclosedherein.

FIG. 22 shows a sensing mechanism 12 h including light gate 226, whichsenses a change in the thickness of the workpiece 218 that saw blade 208is cutting. Light gate 226 is shown in operative use with a table saw 10h of the type explained above. Light gate 226 includes a plurality oflight emitting diodes, (LEDs), 222 mounted to the underside of table224. Positioned above saw blade 208 for receiving the light emitted fromLEDs 222 are a plurality of photo-receivers 228. Photo-receivers 228monitor the amount of light that is emitted from LEDs 222. If the amountof light that is received by photo-receivers 228 is less than a nominalamount or there is a significant change in the amount of light received,the saw blade 208 is shut off. Saw blade 208 may be shut off by a switchor a safety mechanism 14 described herein. In operation, a humanextremity or other object of thickness greater than the workpiece 218,positioned above the workpiece will affect the amount of light that isreceived by photo-receivers 228. In operation, a small amount of lightis emitted around the side and front of the blade 208 because of thenon-circular shape of the blade 208 and the enlarged width of the teethwith respect to the width of the blade 208. If an object that is thickerthan the workpiece 218 comes in close proximity with the saw blade 208,a portion of the light that is emitted around the side and front of theblade 208 is not received by the photo-receivers 228.

FIG. 23 a shows a sensing mechanism 12 i having an ultrasound sensorpanel 236, that senses if a human extremity, is in close proximity to arotating saw blade 208. As shown in FIG. 23 a, the present device isshown in operation with a table saw 10 i as described above. Ultrasoundsensor 236 is generally comprised of a plurality of ultrasound emitters230 and receivers 232 positioned therealong. Panel 236 is positionedabove the top of saw blade 208 so that panel 236 including emitters 230and receivers 232 extend beyond the point where saw blade 208 protrudesfrom planar top surface 224. In operation, a workpiece 218 is movedtoward a rotating saw blade 208 for selective removal of a portion ofthe workpiece 218. As the workpiece 218 is moved toward the saw blade208, ultrasonic emitters 230 send out an ultrasonic signal which isechoed off of the workpiece 218 and saw blade 208 and redirected towardreceivers 232. Receivers 232, monitor the ultrasonic signals todetermine a profile, or height, of the workpiece 218 that is being cut.A change in the thickness, which may be caused by a human extremity,changes the signal that is received by the receivers 232. A change inthe received signal activates a switch 240 which stops the saw blade 208in order to prevent contact of the human extremity with the saw blade208. Again it is appreciated that any safety mechanism 14 disclosedherein may be employed to stop saw blade 208 upon detection from sensingmechanism 12 i.

Referring to FIG. 23 b, a sensing mechanism 12 j including proximitysensing guard 184 for a table saw 10 j is shown in detail. A table sawassembly 10 j, as is well known is comprised of a table 186 having aplanar top surface 188. Formed in table 186 is an elongated slot 190 forreceiving a rotating circular saw blade 192 which is operativelyconnected to a drive (not shown).

Proximity sensing guard 184 is operatively positioned above saw blade192 to prevent accidental contact by the user with the saw blade 192.Proximity sensing guard 184 is composed of a top plate 194 that ispositioned above saw blade 192 and substantially parallel planar topsurface 188. Connected to top plate 194 are a plurality of flexibleconductive sensing wires 196. In preferred operation, an electricalsignal transmitter (not shown) emits a predetermined signal to top plate194 and sensing wires 196. Attached to saw blade 192 is a receiver (notshown) which receives and monitors the signal that is emitted from topplate 194 and sensing wires 196: If an object with a relatively highcapacitance, like the human body comes in contact or close proximitywith sensing wires 196 or top plate 194, the amplitude of the signal isdramatically reduced. When the receiver receives a signal having arelatively low amplitude, indicating a high capacitance object is inclose proximity, a safety mechanism 14 is applied to the saw 10 j toprevent further rotation of the saw blade 192 leading to possiblecontact with a portion of the operator's body.

Moving Hands Away with Inertia

In many typical hand held portable circular saws, the blade is rotatedin a clockwise direction as shown in FIG. 24. The direction of rotationallows the saw blade to smoothly engage the workpiece without causingthe teeth of the saw blade to engage the workpiece and propel the sawforward across the wood. Many commonly available handheld portablecircular saws have a guard that prevents contact between the blade andother objects. However, the nature of a circular saw prevents the guardfrom protecting the saw blade while the circular saw is operating.Simply, the saw blade must be exposed to engage the workpiece.Typically, the guards are rotated into engagement from the rear of thesaw to the front of the saw along a path that is substantially similarto the perimeter of the blade. Many of the guards are biased toward theclosed position by a biasing mechanism.

FIG. 24 shows an exemplary miter saw 10 j which may employ a safetymechanism 14 j in accordance with the present invention. Safetymechanism 14 j limits the area of the blade 304 that is open to contact.Although the following description is directed to a miter saw 10 j, itwill be appreciated that the safety mechanism 14 j may also be used inconjunction with other tools employing a safety guard 308. Guard 308 ispivotally attached to miter saw 10 j and also includes a pivot armassembly 310 linked between miter saw arm 312 and guard 308 to helpensure proper articulation of guard 308 throughout the range of movementof miter saw 10 j.

Safety mechanism 14 j includes a trigger 306 that grasps the side of sawblade 304, which is rotating clockwise, and causes the guard 308 toclose further around the blade 304 to prevent contact with the blade304. The trigger 306 is composed of a coupling mechanism 322 connectedto the guard that is operable to couple the guard 308 to the circularsaw blade 304. Once the coupling mechanism 322 has engaged the circularsaw blade 320, the guard 308 is actuated along direction 316 as shown inFIG. 24. As the guard 308 is actuated along direction 316, the guard 308engages any objects that are contacting the saw blade 304 or areproximate to the saw blade 304 thereby forming a barrier between the sawblade 304 and the operator.

Explained further, if an operator's fingers were detected by for exampleany sensing mechanism 12 described herein, as being in dangerousproximity to the saw blade 304, the guard 308 would immediately coupleto the saw blade 304 causing the guard 308 to move clockwise along withthe saw blade 304. As the guard 308 closes any objects that are in closeproximity to the saw blade 304 are pushed along, and away from dangerouscontact with the saw blade 304. It will be appreciated that trigger 306may alternately engage teeth 320. Safety mechanism 14 j may be used inconjunction with any of the sensing mechanisms 12 disclosed herein.

FIG. 25 shows an exemplary miter saw 10 k which may employ a safetymechanism 14 k in accordance with the present invention. Safetymechanism 14 k alerts the operator of possible contact with saw blade330. Safety mechanism 14 k includes a plurality of flexible wireelements 332 extending from the center of saw blade 330. As saw blade330 is rotated, flexible wire elements 332 are positioned radiallyoutward by centrifugal force to form a circular pattern around therotating saw blade 330. If the operator of the power tool makes contactwith the flexible wire elements 332, the user is alerted that therotating saw blade 330 is in close proximity.

Moving Hands Away without Inertia

An alternative to stopping the active portion of the power tool is tomove the portion of the operator's body that is in dangerously closeproximity to the active portion of the power tool away from the powertool. This methodology does not require a reaction system that mustaccount for the forces associated with stopping a rotating object.However, like a braking system, a hand retraction system must performthe function of moving a portion of the operator's body away from adangerous position with the active portion of the power tool in a veryrapid period of time. In devices such as saws where rapid workpiece feedrates are possible, the portion of the operator's body must be movedaway from the active portion of the power tool very rapidly to preventand/or reduce injury.

FIGS. 26 a and 26 b illustrate a safety mechanism 14 l for rapidlymoving the hand of the user away from a rotating blade 340. Thrust bar342, is generally composed of a first gear 344 rotating with the sawblade 340 and a second gear 346 selectively intermeshed with the firstgear 344. In addition, a link bar 350 extends beyond the perimeter ofthe saw blade 340 positioned adjacent thereto. If a dangerous conditionis detected by for example one of the sensing mechanisms 12 disclosedherein, and it is desirable to move the hand of the operator rapidlyaway from the saw blade 340, a pin 352 thrusts second gear 346 and linkbar 350 into the second first gear 344. The link bar 350 consequentlyrotates in the opposite direction (arrow 354) as the blade 340 from aposition as shown in FIG. 26 a to a position shown in FIG. 26 b in orderto contact the hand of the operator and prevent prolonged contact withthe saw blade 340. It will be understood that alternate gearingconfigurations may be employed having other engaging alternatives whilereaching similar results.

FIG. 27 shows a safety mechanism 14 m operatively associated with tablesaw 10 m. Safety mechanism 14 m includes a kerf guard 370 for preventingcontact between a user and the blade 376 of a table saw 10 m. Kerf guard370 is composed of a kerf plate 372 and an actuation mechanism 374. Inoperation, if it is sensed (by for example one of the sensing mechanisms12 disclosed herein) that a portion of the user's body is in closeproximity to the saw blade 376, the kerf plate 372 is driven from aposition diagrammatically shown in FIG. 28 upward to a protectiveconfiguration as shown in FIG. 29. This configuration prevents theoperator from contacting the blade 376 of the saw 10 m. As shown inFIGS. 28 and 29, actuation mechanism 374 includes cylinders 380 havingshafts 382 which linearly expand therefrom. Shafts 382 may be influencedinto a position shown in FIG. 29 by springs, explosives, fluids or othermeans. It is readily appreciated that actuation mechanism 374 mayalternatively include other fast acting actuation mechanisms such ashydraulic actuators, rack and pinion actuators or any other sufficientmechanism.

FIGS. 30-32 illustrate a safety mechanism 14 n for rapidly moving thehand of the user away from a rotating blade, hinge bar 384. Hinge bar384 is composed of a U-shaped bar positioned around the center of a sawblade 386 and having the distal ends 388 of the bar 384 attached athinge 396 to a portion 360 of the saw 10 n. The proximal portion 390 ofthe U-shaped member is oriented to oppose the distal hinged ends 388.Mounted near the distal ends 388 of hinge bar 384 is an electronicallyactivated charge module 392. Although it is shown that charge module 392is mounted near hinge 396, it will be appreciated that charge module 392may be mounted in any adequate position adjacent to the top of hinge bar384 sufficient to force hinge bar 384 downward.

The operation of safety mechanism 14 n will now be described in greaterdetail. If it is determined by for example one of the sensing mechanisms12 disclosed herein that a dangerous condition exists, charge 392 iselectrically activated. Once the charge 392 has been activated, hingebar 384 is rapidly driven downward by the force of the charge (from aposition diagrammatically depicted in FIG. 30 to a positiondiagrammatically depicted in FIG. 31). In this way, hinge bar 384 swingsin a direction identified by arrow 394 about hinge 396. Consequently,hinge bar 384 contacts the table portion 398 of saw 10 n oralternatively the work-piece 418 thereby displacing saw blade 386 in anupward direction identified by arrow 420 about hinge 422.

With continued reference to FIGS. 30 and 31 and continued reference toFIG. 32, the orientation of bar 384 will be described. Bar 384 ispreferably positioned below arbor 424 and inner and outer blade clamps426, 228. In this regard, bar 384 may swing unimpeded from hinge 396.

It will be appreciated that hinge bar 384 may alternatively comprisedifferent geometries or be arranged in other locations on saw 10 n whilereaching similar results. Furthermore, charge 392 may alternativelycomprise other mechanical or electrical configurations adequate todeploy arm 384 downward with significant force to urge saw blade 386upward about pivot 422.

FIGS. 33 and 34 illustrate a safety mechanism 14 p shown operativelyassociated with saw blade 430. Saw blade 430 is shown removed from amiter saw. Safety mechanism 14 p includes an inflation device 432 and anair bag housing 434 for housing air bag 436. Air bag 436 is deployedfrom housing 434 by inflation device 432 upon sensing of a dangerouscondition by for example one of the sensing mechanisms 12 disclosedherein for rapidly moving the hand of the user away from the rotatingblade 430. Air bag 436 is composed of a rapidly inflatable vessel thatis positioned adjacent to the saw blade 430. If it is desirable to movethe hand of the user away from the saw blade 430, inflation device 432rapidly inflates air bag 436 that expands outward from a position shownin FIG. 33 to a position shown in FIG. 34 to drive the hands of the useraway from the blade 430. Alternatively, a second inflation device 432and air bag 436 may be concurrently employed with safety mechanism 14 p.As a result, an air bag 436 may be placed proximate both sides of sawblade 430 to achieve more uniform push.

FIG. 35 illustrates a safety mechanism 14 q for rapidly moving the handof the user away from a rotating blade 444. Safety mechanism 14 qincludes a charge 446 that is mounted to the lower guard 448 of a mitersaw 10 q. It will be appreciated that safety mechanism 14 q may also beused with a portable circular saw or other saws employing a guard. Thecharge 446 is of the electrically activated type and is oriented to firefrom the rear of the saw 10 q to the front of the saw 10 q. It will beappreciated that charge 446 may alternatively be an explosive device orother suitable device sufficient to move guard 448. If it is determinedby for example one of the sensing mechanisms 12 disclosed herein, that adangerous condition exists, charge 446 is operated. Charge 446 rapidlypropels the lower guard 448 clockwise from an open position (asdiagrammatically depicted in FIG. 35) to a closed position (asdiagrammatically depicted in FIG. 36) to prevent user contact with aportion of saw blade 444.

FIG. 37 illustrates a safety mechanism 14 r shown associated with mitersaw 10 r for rapidly moving the hand of the user away from a rotatingblade 470. Safety mechanism 14 r includes auxiliary upper guard 462rotatably coupled to saw 10 r by way of hinge 464 at the rear of saw 10r. Guard 462 extends around the front of the saw 10 r and includes adownward firing charge device (not specifically shown) mounted thereto.The firing device may include for example an electrically actuatedcharge similar to charge 446 used in relation to safety mechanism 14 q.Alternately, a torsion spring may be implemented at hinge 464 foractuating auxiliary guard 462 from a position shown in FIG. 37 to aposition shown in FIG. 38. In this regard, if a dangerous condition isdetected by for example one of the sensing mechanisms 12 describedherein, the firing device fires causing the auxiliary guard 462 torotate downward from a position diagrammatically shown in FIG. 37 to aposition diagrammatically shown in FIG. 38, moving the operators handaway from the saw blade 470 to prevent further contact therewith. Itwill be appreciated that auxiliary upper guard 462 may comprisealternative shapes which cooperate with a given saw provided guard 462may move unimpeded from an open position (away from a workpiece 476) toa position sufficient to block human interaction with blade 470.

FIGS. 39 a and 39 b illustrate a safety mechanism 14 s shown associatedwith miter saw 10 s for rapidly moving the hand of the user away from arotating blade 502. Safety mechanism 14 s includes projectile magnet504. Projectile magnet 504 is deployed from a large electromagnet 506positioned above the front portion of the blade 502. Projectile magnet504 is coupled to a rigid portion of saw 10 s such as guard 508 or theframe of the saw 10 s whereby it may be sufficiently aimed toward thesaw blade 502 and workpiece 510 interface. If it is determined by forexample one of the sensing mechanisms 12 disclosed herein, that adangerous condition exists, the polarity of the electromagnet 506 isswitched to force the projectile magnet 504 downward in the direction ofarrow 516. The force of the electromagnet 506 and the gravitationalforces combine to increase the momentum of the projectile magnet 504.During operation, the projectile magnet 504 moves from a positionadjacent to electromagnet 506 downward (arrow 516) to a position asshown in 39 b to engage the hand of the user. Once the projectile magnet504 contacts the hand of the user, the momentum of the magnet 504 willdrive the hand of the user away from the blade 502.

Moving Blade Away with Inertia

FIG. 40 is an illustration of a safety mechanism 14 t configured to stopa saw blade of a table saw and effectively manage the conservation ofmomentum associated with rapid deceleration: As shown in FIG. 40, asafety mechanism 14 t is shown to include a frame 520, a collar 522interconnected to frame 520 by a spring member 524, and a blade stop526. Frame 520 is operatively connected to the table saw (notspecifically shown) at point 528 by way of a fastener and throughgearing 530 for selective rotation of safety mechanism 14 t about arbor536 through an infinite number of angles corresponding to an infinitenumber of positions for saw blade 534. In operation, if a dangerouscondition is detected by for example one of the sensing mechanisms 12disclosed herein, worm gear 540 is actuated allowing teeth 542 to urgegearing 530 toward a counterclockwise rotation. Worm gear 540 may beactuated by for example an electric motor. As a result, blade stop 526is actuated counterclockwise thereby allowing foot 546 to engage sawblade 534. Once saw blade 534 has been engaged, the rotational inertiaof saw blade 534 is transferred to linear inertia in the downwarddirection. The linear inertia drives collar 522 in a downward directionaway from the user and possible additional contact with the operator.Spring member 524 is also forced downward to absorb and dissipate aportion of the linear inertia in a controlled manner. Although springmember 524 is depicted as a single leaf spring, it is appreciated thatadditional leaf springs may be employed or alternatively other biasingmembers that may provide a force dissipating function in addition toinhibiting twisting motion between the axis defined by arbor 536 andjoint 532.

Turning now to FIGS. 41 and 42, a safety mechanism 14 u including aratcheting head 550 is shown. As will be described in greater detail,ratcheting head 550 actuates to prevent contact of the user with the sawblade 552. Ratcheting head 550 is composed of a saw guard 554, aratcheting handle 556 and a stop 558. Saw guard 554 includes a gearingportion 560 rotatably attached to the frame of the saw about a fastener562. Stop 558 is positioned along the top front of the saw blade 552,which is rotating clockwise. Ratcheting handle 556 includes a ratchetinggearing portion 548 that is intermeshed with gearing portion 560. Inoperation, if a dangerous condition is detected by for example one ofthe sensing mechanisms 12 disclosed herein, stop 558 engages blade 552.The rotational inertia of the rotating saw blade 552 causes the sawguard 554 to be translated upward from a position diagrammaticallydepicted in FIG. 41 to a position diagrammatically depicted in FIG. 42.As guard 554 is translated upward, the gearing portion 560 operativelyengages the ratcheting gearing portion 548 of handle 556. The ratchetingof gearing portion 560 locks the saw guard 554 at it's highest positionand prevents the saw blade 552 from coming in contact with the operatorshand. Although not specifically shown, it is appreciated that gearingportion 550 is coupled to the frame of a miter saw and cooperates withthe frame to translate downward to a position shown in FIG. 42.

As shown in FIGS. 43 and 44, safety mechanism 14 v is shown. Safetymechanism 14 v includes a strap deployment mechanism 560. Deploymentmechanism 560 includes a strap 562 made of a durable material such asKevlar. Strap 562 passes through a moveable clutch 564 disposed in ahousing arm 566. Clutch 564 is compressed onto the strap 562 with aseries of biasing members 578. Biasing members 578 are preferablysprings adequate to pinch the strap 562 with sufficient force such asbelleville springs. Strap 562 includes an adequate amount of slackcoiled within housing 566 to accommodate a deployment event as will bedescribed in greater detail. Strap 562 is guided through an actuatormount 568 whereby a spring 570 bounds the strap on an upper side. Spring570 is retained in an upward position on an opposite end by a release572. In this regard, strap 562 also is displaced toward release 572.Release 572 is supported for linear movement by a guide 574. A coil 580is disposed in housing 566 adjacent release catch 584. Release catch 584includes a magnet fastened thereon for communicating with coil 580. Inaddition, magnets 582 are disposed in housing 566 to attract catch 584in an at rest position (FIG. 43).

Extension arm 586 is coupled at a dovetail 590 on housing 566. Dovetail590 allows housing 566 to be easily replaced. Extension arm 586 ismounted to trunnion 591 at joint 588. A movable arm 592 extends fromtrunnion 591 and connects at actuator mount 568. The operation of safetymechanism 14 v will now be described. If a dangerous condition isdetected by for example one of the sensing mechanisms 12 disclosedherein, a signal is sent to coil 580. Coil 580 then builds a counterflux opposing magnets 582. The flux pushes the release 572 to the left(from a position diagrammatically depicted in FIG. 43 to a positiondiagrammatically depicted in FIG. 44). The spring 570 with the strap 562releasably attached is rapidly deployed downwardly past the periphery ofthe blade 594. Strap 562 is caught by the teeth of blade 594. Therotation of the blade 594 (clockwise as viewed from FIG. 43) pulls thestrap 562 around its perimeter further engaging additional teeth todistribute the force to stop blade 594. Clutch 564 is concurrentlyengaged providing a clamping force. As blade 594 rotates and pulls anyslack up due to the angle of the arm when spring 570 is deployed, thestrap 562 begins to slide through the clutch 564 with a constant forceto decelerate blade 594. After blade 594 is stopped, the user mustreplace the deployment mechanism 560. As such, the housing 566 is slidlaterally out of dovetail 590 and 598. The assembly of clutch 564 andbellows 596 is then replaced.

Turning now to FIGS. 45 and 46, a safety mechanism 14 w including ashuttle stop 610 is shown. Safety mechanism 14 w is shown in conjunctionwith a miter saw 10 w. As will be described in greater detail, shuttlestop 610 is projected into rotating blade 612 to stop its rotation andthereby prevent contact of the user with a rotating saw blade 612.Safety mechanism 14 w includes a housing 614 having an upper chamber 616and lower chamber 618. A fuse member 620 is positioned in the upperchamber 616. Shuttle stop 610 is positioned in the lower chamber 618 andconnected to the frame of the saw 10 w by a strap 622. A stop pin 624connects the fuse 620 and the biased shuttle 610 together. Shuttle 610is positioned so that the leading edge is adjacent to the upper rearportion of the clockwise rotating saw blade 612. A truss 634 extendsfrom a table portion 636 and supports horizontal support arm 638. Guard640 extends over saw blade 612.

The operation of safety mechanism 14 w will now be described in greaterdetail. If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, a high current charge is sent tofuse 620 by control 628. As fuse 620 is blown, stop pin 624, which wasretained by fuse 620 is urged upwards by biasing member 630 from aposition diagrammatically depicted in FIG. 45 to a positiondiagrammatically depicted in FIG. 46. Once the lower portion of the stoppin 624 has cleared the top of shuttle 624, the shuttle 624 is driveninto the rotating teeth of the saw blade 612 (see FIG. 46) by biasingmember 642. It will be appreciated that other force transfer mechanismsmay be employed to urge shuttle 610 toward blade 612 such as but notlimited to an explosive charge.

Upon deployment, strap 622 uncoils from reel 632 as the teeth of sawblade 612 grasp the shuttle 610 and force the shuttle 610 clockwisearound the perimeter of the blade 612, creating tension on strap 622.Roller 644 guides shuttle 610 toward blade 612 during a deploymentevent. In addition to rapidly decelerating saw blade 612, as strap 622is stretched to a maximum distance, the head of the saw 10 w is drivenupward about pivot by the transfer of the rotational inertia to linerinertia, moving away from the user.

As shown in FIGS. 47 a and 47 b a safety mechanism 14 x including acable stop 646 is shown associated with miter saw 10 x. Again, althoughsafety mechanism 14 x is shown associated with miter saw 10 x, otherpower tools may be employed while reaching similar results. Cable stop646 includes a cable 648 having an engagement member 650 coupledthereto. A first end of cable 648 is coupled at attachment 654 on theupper portion of arm 652. Cable 648 is routed around the rear of arm652.

The operation of safety mechanism 14 x will now be described. If adangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, engagement member 650 is fired upwardinto a gap defined by the space between blade 656 and support 658.During normal operation, blade 656 rotates in a clockwise direction asviewed from FIGS. 47 a and 47 b. As a result, the teeth of blade 656grasp engagement member 650 thereby pulling cable 648 in a directioncounterclockwise around the rear portion of arm 652. Once the slack ofcable 648 is used, cable 648 pulls arm 652 at attachment 654 therebyurging arm 652 upward around pivot 660 from a position asdiagrammatically depicted in FIG. 47 a to a position as diagrammaticallydepicted in FIG. 47 b.

It will be appreciated that engagement member 650 may alternatively befired by other means such as but not limited to an explosive device ormechanical assembly. Engagement member 650 is preferably comprised of ahard pliable material such as hard plastic for example. It will also beappreciated that cable 648 may also be routed around an additional pivotpoint which may comprise a swing arm mounted on support 658.

Turning now to FIGS. 47 c and 47 d, a safety mechanism 14 y employing aleaf spring stop 664 is shown operatively associated with miter saw 10y. Leaf spring stop 664 includes a leaf spring 666, and cable 668. Leafspring 666 is disposed around a mounting hub 670 proximate to theperimeter of saw blade 672. Cable 674 is coupled at eyelet 676 andbiases leaf spring 666 in a direction away from saw blade 672.Deployment actuator 690 is coupled (not specifically shown) to a portionof the miter saw 10 y and maintains adequate tension on cable 674 duringnormal operation. Strap 678 is coupled to leaf spring 666, on a firstend and is mounted to support 680 at spool 682 on an opposite end. Afriction device 684 includes friction block 688 urged against an upperportion of support 680 by biasing member 686. In this way, frictiondevice 684 provides smooth deployment of strap 678 while dissipatingmuch of the stopping energy during a stopping event as will be describedin greater detail.

If a dangerous condition is detected by, for example one of the sensingmechanisms 12 disclosed herein, deployment actuator 690 releases cable674. Deployment actuator 690 may comprise any adequate releasing meanssuch as but not limited to a coil and magnet configuration as discussedin safety mechanism 14 v or a fuse and stop pin configuration asdiscussed in safety mechanism 14 w. Upon release of cable 674, leafspring 666 displaces toward rotating saw blade 672 causing the teeth ofsaw blade 672 to pierce strap 674. In turn, saw blade 672 pulls strap674 in a clockwise direction unraveling spool 682. Friction device 684slows the travel of strap 674 until saw blade 672 comes to a completestop.

Moving Blade Away without Inertia

Turning now to FIGS. 48-50, a safety mechanism 14 aa is shown. Safetymechanism 14 aa is illustrated in cooperation with a table saw 10 aa.Safety mechanism 14 aa includes a displacement mechanism 710 for urgingsaw blade 712 downward to a position below opening 714 of table surface716. Displacement mechanism 710 includes a sufficient displacement meanssuch as, but not limited to, an electronic charge, or a mechanicalactuator for example. It will also be appreciated the displacementmechanism 710 may alternatively be placed below hub 720 of blade 712 forattracting blade 712 toward the displacement mechanism 710. Such aconfiguration may include, but is not limited to electromagnets placedat the displacement mechanism 710 and at the saw blade hub 720.

During operation, if a dangerous condition is detected, by for exampleon of the sensing mechanisms 12 disclosed herein, displacement mechanism710 is actuated. As a result, saw blade 710 moves from a positiondiagrammatically depicted in FIG. 49 to a position diagrammaticallydepicted in FIG. 50. While not specifically shown, it is appreciatedthat the support structure operatively engaged to blade 712 includesvertical displacement ability to accommodate the vertical travel ofblade 712 during a retraction event.

Referencing now FIGS. 51 and 52, a safety mechanism 14 bb is shownoperatively associated with miter saw 10 bb. Safety mechanism 14 bbshows a blade retraction and stop mechanism, linkage 730, that preventscontact of the user with the saw blade 728. Linkage 730 is composed of asaw arm 732, a saw stop 734, a frame 735, a stabilizing link 736 and abrake link 738. Frame 735 is a generally upwardly extending memberhaving a first and a second attachment points. Connected to the firstattachment point is the first end of saw arm 732. The other end of sawarm 732 is connected to a saw blade 728. Connected to the secondattachment point is brake link 738. Brake link 738 is interconnected tosaw arm 732 through stabilizing link 736 and includes a saw stop 734attached to a distal end.

In operation, if a dangerous condition is detected by for example one ofthe sensing mechanisms disclosed herein, the saw stop 734 is actuatedtoward the rotating blade 728 to stop the rotation thereof. Saw stop 734may be actuated by adequate means such as, but not limited to amechanical actuator, or may alternatively be gravity induced forexample. Once the saw stop 734 engages saw blade 728, the rotationalinertia of saw blade 728 is transferred to linear inertia, driving thesaw blade 728 upward. The saw arm 732 and brake link 738 are drivenupward and away from contact with the user. It will be appreciated thatalthough linkage 730 is depicted as a four bar mechanism, other linkagesmay be employed yielding similar results.

Turning now to FIGS. 53 and 54 a safety mechanism 14 cc is shown. Safetymechanism 14 cc is shown operatively associated with miter saw 10 cc.Safety mechanism 14 cc includes a deployment mechanism 740 for advancingarm 742 and therefore saw blade 744 of saw 10 cc upward and away fromcontact with a user. Deployment mechanism 740 is preferably disposed onthe base 748 of table portion 750 adjacent hinge 752.

Deployment mechanism 740 may include any sufficient mechanism capable ofdisplacing arm 742 about pivot 752 such as, but not limited to, anexplosive device, a mechanical spring, compressed gas or the like. Inoperation, if a dangerous condition is detected, by for example one ofthe sensing mechanisms 12 disclosed herein, deployment mechanism 740 isactuated. As such, the force generated onto arm 742 urges arm 742 upwardabout pivot 752 from a position diagrammatically depicted in FIG. 53 toa position diagrammatically depicted in FIG. 54.

Engaging the Blade with a Pawl Stop

FIG. 55 provides a fragmentary view of a safety mechanism 14 dd that maybe adapted for use with a power tool. The safety mechanism 14 ddincludes a pawl 754 pivotally coupled to the housing 760 of the powertool and a biasing device 756 operably coupled to the pawl 754. As willbe further described below, the safety mechanism 14 dd is operable toengage and thus stop the rotary motion of the saw blade 758. While thefollowing description is provided with reference to a safety mechanism14 dd, it is readily understood that the pawl of the present inventionmay be adapted for use with different types of braking mechanisms and/orpower tools.

More specifically, the pawl 754 is pivotally mounted to a frame portion760 of the saw housing on an axle 762 that extends through a bore 764formed in the frame portion of the housing 760. The pawl 754 is adaptedto pivot into the teeth 766 of the blade 758 under the influence ofbiasing mechanism 756. In a preferred embodiment, the biasing mechanism756 is a helical compression spring. Additionally, the pawl 754 isadapted to be self locking, i.e., draw into tighter engagement with theteeth 766 of the blade 758 due to the relative geometry of the blade 758and pawl 754 as they are drawn together.

In a first preferred embodiment, the pawl 754 is composed of a main bodyportion 770 and a contact portion 772. The main body portion 770 definesthe structure of the pawl 754 and adds to the rigidity of the structure.The main body portion 770 of pawl 754 is preferably constructed of apolymeric material having a relatively high hardness, such asacrilonitrile-butadiene-styrene (ABS). However, it is contemplated othermaterials having suitable physical properties may be utilized to formthe main body portion 770 of pawl 754.

The contact portion 772 is formed opposite bore 764 on the pawl 754 andis proximate to the teeth 766 of saw blade 758. The contact portion 772of pawl 754 is preferably constructed of an elastomeric material, suchas polyurethane. However, it is contemplated other materials havingsuitable physical properties may be utilized to form the contact portion772 of pawl 754.

When a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, and it is desirable to stop blade 758,pawl 754 is rotated into engagement with the teeth 766 of blade 758 byinfluence from biasing mechanism 756. Contact portion 772 of the pawl754 engages the blade 758 initially. The elastomeric material of contactportion 772 grasps the blade 758 due to its inherent material propertiessuch as a relatively low shear modulus. As the teeth 766 of the blade758 grasp the contact portion 772 of the pawl 754, the blade 758 beginsto slow down. As the blade 758 is drawn into further engagement with thecontact portion 772 of the pawl 754, the blade 758 is increasinglyslowed. If blade 758 is not completely slowed by the contact portion 772of pawl 754, teeth 766 will engage a plurality of interlocking features774 formed on main body portion 770. Interlocking features 774 extendoutward from the main body portion 770 toward contact portion 772. Asnoted above, the main body portion 770 of pawl 754 is preferablyconstructed of a polymeric material having relatively high hardness.Therefore, as the blade 758 engages the interlocking features 774 of thepawl 754, the relative hardness of the polymeric material forming theinterlocking features 774 will significantly slow and stop blade 758. Inthis way, the improved pawl 754 of the present invention employs thephysical properties of two materials to slow the rotation of the blade758.

Interlocking features 774 also increase the surface area between thecontact portion 772 and the main body portion 770 for purposes ofadhesion. In a preferred embodiment, interlocking features 774 of thepawl 754 are constructed in series of channels extending perpendicularto the plane defined by blade 758. However, it is appreciated thatinterlocking features 774 may be constructed in many different forms andnot depart from the scope of the present invention.

Additionally, it is preferred that contact portion 772 be formed by anovermolding process. In an overmolding process an elastomeric materialis injected onto a plastic body (main body portion 770). Overmoldingallows the two materials (the elastomeric material and the plastic body)to be cohesively attached. Therefore, no external adhesive or fastenersare required.

An alternative preferred embodiment for a safety mechanism 14 dd′ isshown in FIG. 56 wherein like components are referred to with likereference numbers. Safety mechanism 14 dd′ includes an improved pawl754′. In this embodiment, the pawl 754′ is formed as a unitary structureby injection molding of an elastomeric material 778 such aspolyurethane. It is contemplated that pawl 754′ may be formed of otherelastomeric materials and not depart from the scope of the presentinvention. In forming pawl 754′ through injection molding, it isdesirable that the configuration of the mold be such that the fill(flow) path of the injected plastic is perpendicular to the directionthat the pawl 754′ will engage saw 758. The direction of the fill pathis indicative of the direction that most of the polymer chains areoriented. As a result, the material having a fill path that isperpendicular to the direction of impact will have an increased impactstrength, thereby improving the ability of the pawl to slow and/or stopthe rotation of the blade 758.

It is envisioned that the pawl 754′ may further include a fibrousmaterial such as, but not limited to glass, graphite or KEVLARcoinjected with the elastomeric material 778 to form a fiber reinforcedplastic. In this form, both the fibrous material and the elastomericmaterial retain their physical and chemical identities, yet produce acombination of properties that cannot be achieved by either of themindividually. In a fiber reinforced plastic, the fibrous material is theprincipal load carrying members, while surrounding elastomeric material778 keeps the fibrous material in the desired position and orientation.The elastomeric material 778 acts as a load transferring medium betweenthe fibers and also protects them from environmental damage.

In fiber reinforced plastics, the fibers can be materials that are longdirectional filaments, particles that are small non-directional chunksor whiskers that are small directional filaments. In general, fiberstend to have very long lengths with respect to the surrounding material,and tend to have a significantly higher strength along their length.Preferably, fibrous materials include glass fiber, carbon fiber, andkevlar fiber. However, other types of fibrous materials are also withinthe scope of the present invention.

When it is desirable to stop blade 758, pawl 754′ is rotated intoengagement with the teeth 766 of blade 758 by influence from biasingmechanism 756. As pawl 754′ engages blade 758, the elastomeric material778 grasps the teeth 766 of blade 758 due to its relatively high elasticmodulus and relatively low shear modulus. As the teeth 766 grasp thepawl 754′, the blade 758 begins to slow down and is drawn into furtherengagement with the pawl 754′. As teeth 766 of blade 758 engage pawl754′, the fibrous material also engages teeth 766 of blade 758. As teeth766 engage the fibrous material, the speed of blade 758 is increasinglyslowed due to the relatively high strength of the fibrous material. Thecomposite structure of pawl 754′ effectively engages blade 758 throughelastomeric material 778 and effectively slows and stops blade 758through the fibrous material.

Referencing now FIGS. 57 and 58, a safety mechanism 14 ee including analternate pawl 780 is shown. The operation of safety mechanism 14 ee ispreferably employed similar to safety mechanism 14 dd. Pawl 780 iscomprised of a carrier 782 and an engagement portion 784. Engagementportion 784 is preferably made of a thermoplastic with high yieldstrength, but also a high percent elongation to allow it to stretch asit absorbs the energy from the saw blade 786 during a stop event. Thematerial of engagement portion 784 is also conducive to absorb theinitial impact of blade 786 while promoting uniform stopping timesregardless of blade tooth geometry. Carrier 782 is comprised of a rigidlightweight material such as, but not limited to, rigid plastic. Carrier782 is preferably a material conducive to minimize system inertia tofacilitate rapid release of the safety mechanism 14 ee and also providenecessary strength to maintain engagement portion 784 in firm contactwith blade 786. The two piece pawl (i.e. one part carrier 782 and onepart engagement portion 784) allows the user to remove the engagementportion 784 from carrier 782 after a stop event and replace it with anew engagement portion.

Pawl Activation

FIGS. 59 a-61 illustrate exemplary activation systems for deploying apawl type braking system, such as disclosed herein, upon a rotating sawblade. In general, the activation systems include a biasing memberurging the pawl into contact with the active portion of the power tooland a release mechanism coupling the pawl to a portion of the power tool12. The activation system is actuated upon signaling from a sensingmechanism such as described herein, that a dangerous condition exists.In this way, the pawl is uncoupled from a secure position and urged intoengagement with the active portion of the power tool to prevent orreduce possible injuries caused by contact between a portion of theoperator's body and the active portion of the power tool. While theactivation system described herein is shown employing a pawl type stop,it is appreciated that other types of stops adapted to engage the activeportion of a power tool may be utilized with the activation system ofthe present invention.

Turning now to FIGS. 59 a and 59 b, a safety mechanism 14 ff employing amagnetic pawl release 802 is shown. Magnetic pawl release 802 includes abiasing member 804 for exerting a biasing force on pawl 806 to urge pawl806 toward the active portion of the power tool. The biasing member 804of the present invention is preferably a compression spring that ispositioned between a portion of the power tool 10 ff such as frame 810and an opposing face 808 of pawl 806. It is also contemplated that othertypes of biasing members such as leaf springs may be utilized to urgethe pawl into engagement with the active portion of the power tool.Also, it is appreciated that the biasing member may positioned in avariety of positions and still urge the pawl 806 into engagement withthe active portion of the power tool 10 ff such as a saw blade.

The release mechanism 802 is comprised of a first and second oppositelycharged magnets 814, 816 attached to the pawl 806 and a portion of thepower tool 810, respectively. The first magnet 814 is preferably coupledto the rear surface of the pawl 806 and extends in a generally paralleldirection with respect to the rear surface of the pawl 806. The secondmagnet 816 is attached to a portion 810 of the power tool 10 ff andpreferably extends generally parallel to the first magnet 814 when thepawl 806 is in the secured position (FIG. 59 a). In this manner, theface of the second magnet 816 is positioned to align substantially withthe face of the first magnet 814 when the pawl 806 is in the securedposition to optimize the attraction therebetween. The first and thesecond magnets 814, 816, due the opposite polarities, are attracted toone another and provide a second biasing force that is opposite indirection and at least as large in magnitude as the biasing force of thebiasing member 804.

The second magnet 816 also includes a coil 820 formed from electricallyconductive wire disposed around the outer surface of the magnet 816. Thecoil 820 is coupled to a power source (not specifically shown) forcontrolling the magnetic force of the second magnet 816 as is well knownin electromagnetics.

When a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, and it is desirable to activate the pawl806 to stop the active portion of the power tool, an electrical voltageis applied to the wire 820. As the electrical charge is applied, theattractive force of the second magnet 816 is decreased. Once theattractive force of the first and the second magnets 814, 816 is lessthan the biasing force of the biasing member 804, the pawl 806 isreleased from the secured position (as diagrammatically depicted in FIG.59 a) into an engaging position (as diagrammatically depicted in FIG. 59b) with the active portion of the power tool 10 ff.

The amount of time required to release the pawl is preferably minimizedto reduce the overall time required to stop the active portion of thepower tool 10 ff. Therefore, it is desirable to apply a large electricalcharge to the second magnet 816 to allow the attractive force to berapidly reduced or eliminated. It is also appreciated that an electricalcharge capable of changing the polarity of the second magnet 816 couldbe applied to the second magnet 816 causing the first and the secondmagnets 814, 816 to have a repulsion force, further reducing the periodof time required release the pawl 806.

Sensor 822 of the present invention determines if the pawl 806 is in thesecured position and if the coil 820 can be energized. The sensor shownin FIGS. 59 a and 59 b is a Hall-type sensor. The Hall sensor measuresthe magnetic induction field applied in relation to the current flow.Thus, the Hall sensor determines the amount of attraction forces betweenthe first and the second magnets 814, 816 to determine, if the pawl 806is in place and if the coil 820 can be energized. It is appreciated thatother sensors may be employed within the scope of the present invention.

In operation, a controller (not specifically shown) for the power toolmeasures the sensor 822 to determine the location and status of the pawl806. If the pawl 806 is in the secured position, the controller allowsoperation of the power tool 10 ff. In the event of a dangerouscondition, the controller applies an electrical charge to the coil 820of the second magnet 816. Once the coil 820 is electrically charged, theattractive force of the first and second magnets 814 and 816 is reducedand the biasing member 804 urges the pawl 806 into engagement with theactive portion of the power tool 10 ff in a relatively short period oftime.

Turning now to FIGS. 60 a-60 c, a safety mechanism 14 gg employing afuse member 830 is shown. Like components are referred to with likereference numbers as safety mechanism 14 ff. The safety mechanism 14 ggincludes a biasing member 804 urging the pawl 806 into contact with theactive portion of the power tool 10 gg and a fuse member 830 couplingthe pawl 806 to a portion of the power tool 10 gg. The safety mechanism14 gg is designed, upon detection of a dangerous condition by forexample one of the sensing mechanisms 12 disclosed herein, to uncouplepawl 806 allowing the pawl to engage the active portion of the powertool 10 gg to prevent or reduce possible injuries caused by contactbetween a portion of the operator's body and the active portion of thepower tool 10 gg. While the activation system of the present inventionis shown employing a pawl type stop, it is appreciated that other typesof stops adapted to engage the active portion of a power tool may beutilized with the activation system of the present invention.

Safety mechanism 14 gg including fuse member 830 extends from pawl 806to a portion of the power tool 10 gg. The fuse member 830 is generallycomprised of an electrically conductive wire 832 formed into a loopshape and a crimp portion 834 coupling the ends of the wire together.The loop shape of the fuse member allows the fuse to be positionedaround a desired point on each of the power tool 10 gg and the pawl 806as needed. The electrically conductive wire 832 is formed of a materialthat is deformable upon application of a relatively large electricalcurrent to the wire 832. The crimp portion 834 is generally a unitarymember that is positioned over the ends of the wire 832 and deformed tomechanically couple the first and second ends of the wire 832 together.The crimp portion 834 may be formed of any of a variety of materialsexhibiting greater strength than the wire 832.

When a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein and it is desirable to activate the pawl806, a relatively large electrical current is applied by controller 838to the fuse member 830. Upon application of the electrical current, thefuse member 830 begins to weaken mechanically. Once the biasing force ofthe biasing member 804 exceeds the tensile strength of the electrifiedfuse member 830, the pawl 806 is urged toward the active portion of thepower tool (FIG. 60 b).

The electrical activation of the present invention allows the rapidrelease of the pawl stop of the braking system. Rapid release of thepawl 806 reduces the overall time required to stop the active portion ofthe power tool. Thus, the possibility for injurious contact between theactive portion of the power tool and a portion of the operator's body isreduced or eliminated.

FIGS. 61 a-61 c illustrates a safety mechanism 14 hh including analternative fuse member 830′. Fuse 830′ includes a unitary stamped metalbody portion. Mounting bores 818 are disposed on opposite ends of fuse830′ for mounting to pawl 806 and tool 10 hh respectively. The operationof safety mechanism 14 hh is similar to the operation of safetymechanism 14 gg. Fuse 830′ presents several advantages over atraditional wire fuse. In this regard, no additional assembly is neededwith unitary fuse member 830′. In addition, the length of the fuse 830′is controlled by tooling rather than during assembly of the fuse 830′.

A second embodiment of a pawl type activation system is shown in FIGS.62 a-62 b. Safety system 14 ii includes a biasing member 840 urging apawl 842 into contact with the active portion of the power tool and anactivation system 844 coupling the pawl 842 to a portion of the powertool. The safety system 14 ll is designed, upon signaling from forexample a sensing mechanism 12 disclosed herein, to uncouple the pawl842 allowing the pawl 842 to engage the active portion of the power toolto prevent or reduce possible injuries caused by contact between aportion of the operator's body and the active portion of the power tool.While the activation system 844 of the present invention is shownemploying a pawl type stop, it is appreciated that other types of stopsadapted to engage the active portion of a power tool may be utilizedwith the activation system of the present invention.

The activation system 844 includes a rotatable latch 846 engaging afinger portion 848 of the pawl 842 and first and second solenoids 850,852 actuating the latch 846. The latch 846 is rotatably coupled about anaxis of rotation to a portion of the power tool to support the latch 846and the pawl 842 in the secured position. The latch 846 includes anengagement arm 856, a support arm 858 and an activation arm 860extending generally from the axis of rotation in a “T” shapedconfiguration. The engagement arm 856 of the latch 846 operativelyengages finger portion 848 of the pawl 842. The support arm 858 engagesthe first solenoid 850 to restrain the pawl 842 in the secured positionvia the engagement arm 856. The activation arm 860 is in contact withthe second solenoid 852 which operatively rotates the latch 846 to allowthe pawl 842 to engage the active portion of the power tool.

The first solenoid 850 operates as a protective device to preventinadvertent activation of the pawl 842. In operation, the plungerportion 862 of the first solenoid 850 is placed in the extended positionto engage the support arm 858 of the latch 854 during the initialunstable operation of the power tool. The plunger portion 862 of thesolenoid 850 prevents the latch 854 from rotating and releasing theengagement arm 856 from engagement with finger 856 of the pawl 842.

Once the power tool has stabilized, the second solenoid 852 ismagnetically coupled to activation arm 860 by an electromagnet forpreventing rotation of the latch 854 and release of the pawl 842. Next,the plunger portion 862 of the first solenoid 850 is retracted. If adangerous condition has been detected by for example one of the sensingmechanisms 12 disclosed herein and it is desirable to release the pawl842, the magnetic coupling between the activation arm 860 and the secondsolenoid 852 is reduced. Once the magnetic coupling is reduced, latch846 rotates and the biasing member 840 urges the pawl 842 about pivot864 (from a position diagrammatically depicted in FIG. 62 a to aposition diagrammatically depicted in FIG. 62 b) into engagement withthe active portion of the power tool. The electromagnetic coupling ofthe pawl 842 allows the pawl 842 to be activated relatively rapidly.Rapid activation of the pawl 842 reduces the overall time required tostop the active portion of the power tool. Thus, the period of time thatinjurious contact may take place between the active portion of the powertool and a portion of the operator's body is also reduced.

In the event of interruption to the electrical power of the activationsystem 844 the pawl 842 will not engage the active portion of the powertool. Once electrical power is removed from the activation system 844,the plunger portion 862 of the first solenoid 850 will return to theextended position. In the extended position, the plunger 862 preventsrotation of the latch 860, which will release the pawl 846. Once adeployment event has occurred, pawl contacts 866 detach from triggerprinted circuit board 868. Pawl contacts 866 must be reattached totrigger printed circuit board 868 after a deployment event.

Strap Stops

Braking systems are well known for use with many devices. Conventionalbraking systems either engage the portion of the device that is desiredto be stopped or a segment of the device that is connected to theportion of the device that is desired to be stopped. However, manybraking systems require a lengthy period of time to stop the portion ofthe power tool. Braking systems in power tools must be able to stop theactive portion of the power tool in a very rapid period of time toreduce and/or eliminated the amount of injury to the operator of thepower tool due the relatively high speeds of the power tool and thedangerous nature of the active portion of the power tool.

Turning now to FIGS. 63 a and 63 b, a safety mechanism 14 jj employing astrap stop 870 is shown operatively associated with miter saw 10 jj. Theexemplary power tool embodied herein is a miter saw, however it isappreciated that the safety system of the present invention may beadapted for use with a variety of power tools. In general, miter saw 10jj includes a strap 872 employed to provide braking force uponengagement with a saw blade not specifically shown. Strap 872 ispreferably made of a strong flexible material such as Kevlar. A frictionstopping device 898 includes a friction disk 882 and drum 876.

Housing 878 includes strap 872 shown wound around drum 876 which isrotatably disposed on shaft 880. Strap 872 is wrapped around drum 876 insufficient supply to accommodate a single blade stop event. Frictiondisk 882 is fixed from rotation with drum 876. A spring 894 biasesfriction disk 882 into engagement with drum 876. In a safety event thestrap 872 is moved into engagement with a saw blade causing the strap872 to be pulled by the blade. As such, the strap 872 will uncoil fromdrum 876 as the drum 876 rotates in a counterclockwise direction asviewed from FIG. 63 a. The friction disk 882 provides a predeterminedamount of friction to resist excessive rotation of the spool 876 in adeployment event. Friction disk 882 includes friction material disposedthereon for cooperating with biasing member 894 urging friction disk 882into drum 876. It is appreciated that alternatively or additionally,friction material may be incorporated on the engaged surface of drum876. Friction spool 876 is preferably placed in a location favorable tounabated unwinding. Accordingly, the friction provided by theinteraction between friction disk 882 and drum 876 generates the forcenecessary to stop rotation of the saw blade.

Deployment mechanism 900 includes carrier 902 supporting two edges ofthe strap 872. The center of the strap 872 is unengaged and suspendedbetween the two edges 904. Edges 904 are secured in channels providingadequate resistance to the removal of the strap 872 laterally orperpendicularly to the straps orientation. This resistance however isinsignificant relative to the friction provided by friction disk 882.

The strap carrier 902 is preferably deployed by one of the followingdeployment means. A preferred embodiment includes a spring 904, firstand second magnets 906, 908 and a coil 910. The spring 904 is compressedwhich provides the deployment force. First magnet 906 is coupled to thestrap carrier 902 and the second magnet 908 is coupled to the housing878. Second magnet 908 exerts sufficient attractive force on the firstmagnet 906 to overcome the spring 904. The coil 910 is used to degradethe field in the fixed magnet 908 so that at the desired time, thespring force overcomes the magnetic force and the strap 872 moves up toengage the saw blade. Alternatively, the first and second magnet 906 and908 may be replaced with a fuse wire such as disclosed in relation tosafety mechanism 14 w for example. While not specifically shown inrelation to this embodiment, a first end of the fuse wire may beattached to the strap carrier 902 and a second end attached at twoelectrical contact points on the housing 878. A small gap extendsbetween the two electrical contact points. When sufficient voltage isapplied at the two contacts, a large current is induced in the fuse wireheating and weakening the segment of wire between the contacts. Thespring force then breaks the fuse wire and the strap carrier 902 isreleased to engage the saw blade 874. It will be appreciated that otherdeployment mechanisms may be employed within the scope of the presentinvention.

When a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, coil 910 degrades the magnetic fieldbetween magnets 906 and 908 allowing spring 904 to force carrier 902toward the saw blade into the direction depicted by arrow 912, and thusstrap 872 into the saw blade. In this regard, the blade teeth engage thecenter unsupported section of the strap 872 causing the blade teeth topierce the strap 872. Once the strap 872 is forcefully engaged to theblade teeth, the strap 872 is pulled out of the housing 878, the slackis used and the braking force generated by the friction clamping device898 slows the blade 874 to a stop as the strap 872 unwinds from drum876.

In an alternate embodiment shown in FIG. 63 c, safety mechanism 14 jj′includes strap 872 routed through a freely pivoting friction clampingdevice 884. Like reference numbers are used to designate likecomponents. Strap 872 is wrapped around spool 914. Clamping device 884includes a pivoting steel block 886 on a large shaft 888, such as 0.75inch diameter, with a plate 890 attached by conventional fasteners 892.The strap 872 is routed to pass between the plate 890 and the block 886.Plate 890 is secured to the steel block 886 with a predetermined amountof clamping force providing a frictional force to resist movement of thestrap 872 through clamp device 884. A sufficient amount of slack isarranged in the strap 872 enabling the strap 872 to be wrapped aroundthe blade 874 as necessary to generate a sound engagement between thestrap 872 and the blade teeth.

As with safety mechanisms 14 jj and 14 jj′, an adequate amount of strap872 is wound around drum 876 and 914 to provide enough stopping travel.Furthermore, subsequent to a stopping event, strap 872 is preferablyreplaced by an unused strap and recoiled through the respective stoppingmechanisms 14 jj, 14 jj′.

Swing Blade Away From Contact

Referencing now FIGS. 64 a-64 j, safety mechanisms 14 kk-14 ll′ aredescribed incorporating apparatus sufficient to displace a rotating sawblade and support arm about a pivot point on the saw structure. Theresulting motion causes the saw blade to swing upwards and out ofcontact with the user. Although the exemplary descriptions are directedtoward a miter saw, it will be appreciated that other power tools may beemployed within the scope of this disclosure.

Safety mechanism 14 kk as shown in FIGS. 64 a and 64 b includes swingarm 920 having fore and aft finger supports 922 and 924 respectivelyextending therefrom. Swing arm 920 is rotatably coupled at pivot gear930 to frame 926 of miter saw 10 kk. Support bar 928 connects fingersupports 922 and 924. Saw blade 932 is coupled to a distal end of swingarm 920. Gear 934 is meshed for rotation with pivot gear 930 andcooperates therewith upon actuation of safety mechanism 14 kk during asafety event.

The operation of safety mechanism 14 kk will now be described in greaterdetail. If a dangerous condition is detected by for example one of thesafety mechanisms 12 disclosed herein, gear 934 is activated in acounterclockwise direction (arrow 936). As a result, swing arm 920swings upward and away from contact with the user from a position asdiagrammatically depicted in FIG. 64 a to a position as diagrammaticallydepicted in FIG. 64 b. Gear 934 is preferably actuated with a motor (notspecifically shown) with sufficient speed to rotate swing arm and thussaw blade 932 out of contact with the user in a minimal amount of time.It will also be appreciated that meshed gears 934 and 930 may alsocomprise other explosive, mechanical or electromechanical devices withinthe scope of this invention.

Turning now to FIGS. 64 c and 64 d, safety mechanism 14 kk′incorporating cable 938 is shown. Cable 938 includes a first end havinga loop 940 and an opposite end spooled around drum 942. An intermediateportion of cable 938 passes through friction device 944. Friction device944 includes a friction block 946 biased against support arm 948 bybiasing member 950.

If a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, loop 940 of cable 938 is thrown towardrotating saw blade 952 by deployment module 954. In this way, loop 940grasps the teeth of rotating saw blade 952 thereby uncoiling cable 938from drum 942. Concurrently, friction device 944 slows the momentum ofcable 938 allowing saw blade 952 to come to a complete stop. The angularmomentum of rotating saw blade 952 causes arm 956 to rotate upward aboutpivot 958 from a position as shown in FIG. 64 c to a position shown inFIG. 64 d. It will be appreciated that an adequate amount of cable isstored around drum 942 to sufficiently uncoil during a stop event.Deployment module 954 may comprise any sufficient means to thrust loop940 toward saw blade 952 such as but not limited to an explosive firingdevice.

FIGS. 64 e and 64 f illustrate safety mechanism 14 kk″ having analternative configuration from safety mechanism 14 kk′. As such, likecomponents will be referred to with like reference numerals. Frictiondevice 944′ is mounted for cooperation with arm 956′. Furthermore, drum942 is mounted at an upper portion of support arm 948′.

The operation of safety mechanism 14 kk″ is substantially similar tosafety mechanism 14 kk′. The alternate placement of friction device 944and drum 942 provides different braking and packaging advantagesassociated with a given miter saw configuration.

With reference to FIGS. 64 g and 64 h, safety mechanism 14 ll will bedescribed in cooperation with miter saw 10 ll. Safety mechanism 14 llincludes deployment wedge 960 and magneto-rheological fluid shock 962.Deployment wedge 960 is preferably slidably coupled to arm 964. Arm 964is pivotally coupled to frame 966 at a first end and includes a sawblade 968 coupled at an opposite end.

If a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, wedge 960 is deployed in a directiondenoted by arrow 970 toward an upper portion of magneto-rheologicalshock 962. The force created from the impact of wedge 960 into shock 962causes rod 974 to expel from shock 962 causing arm 964 and thus sawblade 968 to swing upwardly about pivot 972. Upon articulation of arm964 about pivot 972, shock 962 expands from a position asdiagrammatically shown in FIG. 64 g to a position as diagrammaticallyshown in FIG. 64 h. Once shock 962 has expanded to the position shown inFIG. 64 h, a current is applied to the magneto-rheological fluid withinshock 962 causing the shock to lock in an expanded position. As is wellknown, a magneto-rheological fluid damper utilizes a fluid which canhave the viscosity altered through the application of a magnetic field.It will be appreciated that alternate configurations may be employed tomaintain arm 964 in the position shown in FIG. 64 h, for example, amaster cylinder may be incorporated to fill a reservoir within shock 962to lock the arm in a safe position. In addition, a biasing swing arm maybe incorporated to encourage retention of cylinder 962 in an expandedposition. In this way, a biasing swing arm may be employed between rod974 and shock 962 to allow movement of rod 974 out of cylinder 962 in afirst expanded position and resist movement of rod 974 back into shock962.

Safety mechanism 14 ll′ incorporated into saw 10 ll′ is depicted inFIGS. 64 i and 64 j and includes expansion shock 976. Expansion shock976 includes first and second extension rods 980 and 982 selectivelyextending therefrom. Expansion shock 976 is pivotally coupled to arm 978at pivot 984. During a safety event, rod 982 is expelled from rod 980thereby rotating arm 978 and thus saw blade 986 up and away from contactwith a user.

Rod 982 may be expelled by any sufficient means such as but not limitedto an explosive propellant for example. It should be noted that althoughsafety mechanism 14 ll′ is depicted as incorporating rod 980 and 982, analternative amount of rods may be incorporated while reaching similarresults. It is also appreciated that a magneto-rheological shock or abiased pivot arm as described in conjunction with safety mechanism 140may also be employed to maintain arm 978 in an upward orientation.

Projectile stops

Turning now to FIGS. 65 a and 65 b, a safety mechanism 14 mm is shown.Safety mechanism 14 mm includes a projectile stop 1020, for selectivelystopping a circular saw blade 1022 in a short period of time. In thiscase the angular momentum is transferred to an object that is notconnected to the saw, and thus does not create any unwanted linearmomentum leading to movement.

In general, projectile stop 1020 includes a firing device 1024 forexpelling a projectile 1026. In operation, projectile 1026 is launchedinto the saw blade 1022 in an opposite direction of rotation of the sawblade 1022. When the projectile 1026 contacts the saw blade 1022, thekinetic energy and the rotational inertia of the blade 1022 are opposingand thus cancel each other. If the energy of the projectile 1026 matchesthe rotational inertia of the saw blade 1022, the blade 1022 will becompletely stopped.

Firing device 1024 may comprise any deployment means sufficient todirect projectile 1026 toward blade 1022 with sufficient momentum. Inthis way, firing device may include an explosive device or a mechanicalspring assembly for example. Projectile 1026 may comprise any suitablematerial having a mass sufficient to create adequate momentum upon afiring event to null the angular momentum of blade 1022.

The operation of projectile stop 1020 will now be described in greaterdetail. If a dangerous condition is detected by, for example, one of thesensing mechanisms 12 disclosed herein, firing device 1024 is activated.Projectile 1026 in turn is fired into the teeth of blade 1022 therebycountering the angular momentum of blade 1022 bringing the blade 1022 toa stop in a short period of time. Concurrently, power is cut from saw10. An exhausted projectile stop 1020 must be replaced after a firingevent with a new projectile stop.

Engage Blade not Teeth

FIGS. 66 a-66 c show safety mechanism 14 nn having a pin stop 1036, tostop a saw blade 1038 in a very short period of time. Safety mechanism14 nn is described with respect to a miter saw but it will beappreciated that safety mechanism 14 nn may be employed with other sawsand power tools. Pin stop 1036 is compressed of a channel 1040 that isdisposed around the perimeter of the saw blade 1038 and connected to theframe (not shown) of the saw. Channel 1040 also includes a bore 1042formed through both sides of the channel 1040 for operatively receivingpin stop 1036. If the operator or other system desires to stop the bladein a short period of time, a pin 1044 is driven into the bore 1042 andengages one of a plurality of holes 1046 along the edge of the saw blade1038 to prevent further movement of the blade 1038. Explained further,pin 1044 engages blade 1038 along a outer path 1045 thereof. The blade1038 continues to rotate until pin 1044 falls through an adjacent hole1046. Once pin 1044 is thrust through a hole 1046 (FIG. 66 c), blade1038 immediately stops. Alternatively, if a blade not specificallyhaving holes 1046 arranged around the perimeter of the blade, the pin1044 may be driven into the teeth of the blade to stop further rotationof the blade 1038.

With specific reference to FIGS. 66 b and 66 c, the operation of safetymechanism 14 nn will be described in greater detail. If a dangerouscondition is detected by for example one of the safety mechanismsdisclosed herein, pin 1044 is rapidly actuated toward saw blade 1038consequently engaging one of the holes 1046 incorporated in saw blade1038 thereby immediately stopping the rotation thereof. Pin 1044 may bedeployed by any sufficient means such as but not limited to biasingmember 1048.

FIGS. 67 a and 67 b illustrate another safety mechanism 1400 having acam stop 1050 to stop a saw blade 1066 in a very short period of time.Cam stop 1050 is generally composed of a electric module 1052, a fuse1056 connected to a first end of the electric module 1052, a spacer 1054connected to the other end of the fuse 1056, a first biased cam 1058 andsecond biased cam 1060 retained in a neutral position by the spacer1054. In operation, the electric module 1052, upon signal from anotherdevice (such as a sensing mechanism 12 disclosed herein) releases a highcurrent charge to fuse 1056. Once fuse 1056 is blown, spacer 1054 nolonger restrains cams 1058 and 1060. Upon release from spacer 1054, cams1058 and 1060 are rotated inward (in a direction depicted by arrows1068) by torsional springs 1062 and 1064 to stop saw blade 1066.

FIGS. 68 a and 68 b illustrate a safety mechanism 14 pp including airbag device 1074 for rapidly moving the hand of the user away from therotating blade 1070. Air bag 1074 is disposed proximate spindle 1080 andinner and outerblade clamps 1082, 1084. Air bag 1074 is compressed of arapidly inflatable vessel 1072 that is positioned adjacent to the sawblade 1070 and an inflation device 1076 for rapidly inflating theinflatable vessel 1072.

Inflation device 1076 is preferably configured to inflate vessel 1072with a fluid such as air. Inflation device 1076 may also be configuredto inflate vessel 1072 with other fluids such as water, gel or the likewithout departing from the scope of the invention.

The operation of safety mechanism 14 pp will now be described in greaterdetail. If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein and it is desirable to move thehand of the user away from the saw blade, inflation device 1076 isoperated. Inflation device 1076 rapidly inflates a vessel 1072 thatexpands outward from the tool (from a position diagrammatically depictedin FIG. 68 a to a position diagrammatically depicted in FIG. 68 b) todrive the hands of the user away from the blade 1070. In this way,vessel 1072 preferably expands to a distance greater than the length ofblade 1070 to inhibit user interface with the teeth of blade 1070.

It will be appreciated that inflation device 1076 may alternatively bemounted in other areas adjacent to the saw blade 1070 such as forexample to a portion of the frame. In this way, inflation device 1076may be arranged to deploy vessel 1072 downward at the hand or extremityof the user to bat the same away from contact with the saw blade 1070.

Referencing now FIG. 69, a safety mechanism 14 qq including fluid bag1090 is shown. Fluid bag 1090 is composed of at least one inflatablevessel 1092 positioned adjacent to saw blade 1100. Saw blade 1100 isshown disposed on arbor 1102 between inner and outer blade clamps 1104and 1106. Fluid bag 1090 contains magneto-rheological fluid. Once thesaw blade 1100 is desired to be stopped, a current is applied to themagneto-rheological fluid, the inflatable vessel 1092 inflates andcontacts the saw blade 1100. Consequently, the friction generatedbetween fluid bag 1090 and saw blade 1100 causes the saw blade torapidly slow to a complete stop.

Not Engaging Blade

FIG. 70 shows a safety mechanism 14 rr. Safety mechanism 14 rr includesa jam stop 1116, to stop a saw blade 1118 in a very short period oftime. Jam stop 1116 is composed of a first gear 1120 mounted to therotating arbor (not specifically shown) and a second gear 1122 drivinglyconnected to the first gear 1120 and a wedge 1124. The first gear 1120and second gear 1122, rotate in opposite directions to one another, dueto the meshing of the gears.

If a dangerous condition is detected by, for example one of the safetymechanisms 12 disclosed herein, biasing member 1126 drives wedge 1124 ina direction depicted by arrow 1130 between the intermeshing gear teethof the first gear 1120 and the gear teeth of the second gear 1122. Wedge1124 efficiently stops the rotation of saw blade 1118 by precludingsubsequent rotation of first and second 1120 and 1122. Tip 1132 of wedge1124 is comprised of a rigid material suitable to effectively dissipatethe rotational energy and momentum of saw blade 1118.

It will be appreciated that jam stop 1116 may comprise alternativeconfigurations within the scope of the present invention. For example, ahub may be mounted to gear 1120 or 1122. In this regard, wedge 1124 maybe configured to engage a hub extending from gear 1120 or 1122. The hubmay also include protrusions extending around a circumference thereof.In this configuration, wedge 1124 is preferably comprised of a pliablematerial such as plastic allowing for the protrusions of the hub to diginto wedge 1124 in a stop event. Explained further, in a stop event,wedge 1124 is actuated into the hub causing protrusions to dig into thewedge 1124 until the hub stops rotating. In this manner, the gear havingthe hub disposed thereon stops rotating consequently stopping rotationof blade 1118.

Brake-Away Features for Braking Configurations

According to many of, the safety mechanisms 14 employed herein, thesafety mechanisms 14 are configured to rapidly stop a saw blade fromrotating. In this manner, abruptly stopping a saw blade from rotatingmay cause damage to the motor of the saw 10 or other internal gearingsuch as the spindle for example. The following drive system protectionmechanisms 16 are employed to limit the force a saw blade motor andrelated drive system must endure during a rapid stopping event. Ingeneral, the protection mechanisms 16 may be used concurrently with anysensing mechanism 12 or safety mechanism 14 disclosed herein. Protectionmechanisms 16 include break away features which allow the saw blade tostop rapidly (upon actuation of a safety mechanism for example), whileallowing the drive system to continue rotating.

Referencing FIG. 71, a protection mechanism 16 a is shown operativelyassociated with a miter saw 100 a. Again, while protection mechanism 16a is shown associated with a miter saw, it will be appreciated thatprotection mechanism 16 a may be employed with other power tools withinthe scope of this invention. Drive system 1156 of miter saw 10 aincludes a motor 1140 operatively coupled for rotation with a bladearbor shaft 1142. Blade 1144 is fixed for rotation between inner andouter blade clamps 1146 and 1148 respectively. Inner blade clamp 1146includes a key 1150 extending into complimentary bores 1152 withinspindle 1142. In this way, blade clamps 1146 and 1148, in turn, coupleblade 1144 for rotation with spindle 1142.

During a stopping event, such as by implementation of one of the safetymechanisms 14 disclosed herein, blade 1144 is rapidly stopped.Concurrently, key 1150 shears from inner blade clamp 1146 therebyallowing the drive system 1156 including spindle 1142 and motor 1140 tocontinue rotating. As a secondary measure, the power may be cut to thesaw 100 a after a stopping event allowing the drive system 1156 toslowly spin to a complete stop. Nonetheless, in either scenario, innerand outer blade clamp 1146, 1148 together with blade 1144 remain stoppedas drive system 1156 continues to operate or slowly comes to a stop.

After a stop event, the existing inner blade clamp 1146 is discarded anda new inner blade clamp having an integral key 1150 is employed. Key1150 is preferably made of a material, such as but not limited toaluminum for example, having sufficient rigidity to maintain the bladeclamp in a coupled relationship with the spindle 1142 during operationwhile also having characteristics allowing the key 1150 to be shearedfrom the blade clamp 1146 during a stopping event. It is appreciatedthat key 1150 may also include other details allowing for a selectivelyfixed relationship between the blade clamp 1146 and spindle 1142. Inaddition, it will be appreciated that outer blade clamp 1148 mayalternatively be keyed to spindle 1142 yielding similar results.Moreover, while protection system 16 is described as cooperating with asafety mechanism 14 that negotiates the saw blade 1144 to stop the same,protection system 16 may also be employed to a safety system 14 which isalternatively configured to manipulate the saw clamp.

Turning now to FIG. 72, an alternative protection mechanism 16 b isshown incorporated with power tool 100 b. Like reference numerals willbe used to designate like components of protection mechanism 16 a. Innerblade clamp 1166 is keyed to outer blade clamp 1168 by feature 1170.Feature 1170 may include threaded fasteners such as screws oralternatively pins. In this way, feature 1170 is configured to shearupon a stopping event such that inner and outer blade clamp 1166, 1168may rotate or stop independently of each other. Feature 1170 mayalternatively be an adhesive bond capable of separating inner and outerblade clamp 1166, 1168 upon a stopping event. A blade bolt 1172 clampsinner blade clamp 1166 to the spindle 1142.

During a stopping event, blade 1176 is rapidly stopped by for exampleone of the safety mechanisms 14 disclosed herein. Rapid stopping ofblade 1176 causes feature 1170 to shear thereby uncoupling the innerblade clamp 1166 from the blade 1176 and outer blade clamp 1168. In thisregard, drive assembly 1156 including spindle 1142 and motor 1140 arefree to continue rotation while blade 1176 is stopped minimizing injuryto the operator and the power tool 100 b. Lip 1180 extends from bladebolt 1172 outwardly beyond the inner diameter of outer blade clamp 1168.During a stop event, outer blade clamp 1168 and blade 1176 may have atendency to travel toward blade bolt 1172. Lip 1180 retains outer bladeclamp 1168 between blade bolt 1172 and inner blade clamp 1166 precludingthe outer blade clamp 1168 and blade 1176 from falling off the spindle1142.

In an additional embodiment, biasing members may be employed betweeninner blade clamp 1166 and blade 1176 for further urging blade 1176 andouter blade clamp 1168 away from inner blade clamp 1166.

Miscellaneous Braking

Referencing FIG. 73 safety mechanism 14 ss having a secondary hub 1180is shown operatively associated with miter saw 10 ss. Secondary hub 1180is coupled for rotation with spindle 1188 and is disposed adjacent innerblade clamp 1182. Blade 1186 is mounted for rotation between inner andouter blade clamp 1182 and 1184. Protrusions 1190 extend radially fromsecondary hub 1180. As will be described in greater detail, stoppingdevice 1192 is disposed adjacent hub 1180 and is arranged to linearlyengage protrusions 1190 of hub 1180 during a stopping event.

If a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, stopping device 1192 is actuated intoprotrusions 1190 extending from hub 1180. Stopping device 1192 may beactuated by a firing device or a mechanical actuator for example.Further, stopping device 1192 is preferably comprised of a pliablematerial such as plastic sufficient to dig into protrusions 1190 duringa stopping event. Hub 1180 and stopper 1192 must be replaced after astopping event.

It will be appreciated that stopper 1192 may alternatively be configuredto engage inner blade clamp 1182 directly. In this way, inner bladeclamp 1182 may have a friction surface disposed on an outercircumference thereof for stopper 1192 to engage. Additionally, safetymechanism 14 ss may also include a friction or keyed mating surfacebetween the inner blade clamp 1182 and blade 1186 to further encourageblade 1186 to stop with inner blade clamp 1182 during a stop event.

Miscellaneous Stop

Turning now to FIGS. 74 a and 74 b, a safety mechanism 14 tt employingnautilus stop 1196 is shown. Nautilus stop 1196 includes an involutespline shaped cam member 1198 disposed adjacent a saw blade 1200. Abiasing member 1206 biases cam 1198 into the position diagrammaticallydepicted in FIG. 74 b. In this regard, cam 1198 is retained or otherwisemaintained in the position shown in FIG. 74 a by a latch 1208 duringnormal operation of the tool. During a stop event, as will be describedin greater detail, cam 1198 rotates about axis 1202 in acounterclockwise direction from the position as diagrammaticallydepicted in FIG. 74 a to the position diagrammatically depicted in FIG.74 b. Cam 1198 is made of a strong material sufficient to absorb therotational energy from blade 1200. Similarly, the material of cam 1198must be sufficiently rigid to bring blade 1200 to a complete stop.Surface 1204 of cam 1198 is shown having a smooth radial contour,however, surface 1204 may alternatively have an irregular surface toencourage adequate gripping action between the cam 1198 and blade 1200.

The operation of safety mechanism 14 tt will now be described. If adangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, latch 1208 releases cam 1198 from theposition shown in FIG. 74 a. As such, biasing member 1206 urges cam 1198in a counterclockwise direction toward rotating saw blade 1200. Uponcontact, the rotational energy of the blade 1200 (rotating in aclockwise direction) will encourage cam 1198 to further rotatecounterclockwise progressively increasing engagement and deceleration ofblade 1200. It will be understood that cam 1198 may comprise othergeometries without departing from the scope of this invention.Additionally, it is appreciated that additional cams 1198 may beconcurrently employed around the periphery of saw blade 1200.

Turning now to FIGS. 75 a and 75 b, a safety mechanism 14 uu includingcam actuated brake 1220 is shown. An eccentric cam 1222 is fixed forrotation with blade 1224. Cam actuated brake 1220 includes a camfollower 1226 positioned adjacent the cam 1222 and near the smallestradius (as shown in FIG. 75 a). Cam follower 1226 is disposed in anaxially displaced position with respect to cam 1222 during normaloperation of the tool. A brake arm 1230 is coupled to cam follower 1226and extends in a direction generally tangential from blade 1224.

The operation of safety mechanism 14 uu will now be described in greaterdetail. If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, cam follower 1226 is displacedaxially toward blade 1224 whereby cam 1222 and cam follower 1226 areengaged. Axial displacement of cam follower 1226 may be achieved by anysufficient means such as a mechanical actuator or explosive firing eventfor example. Accordingly, clockwise rotation of cam 1222 will urge camfollower from a position diagrammatically depicted in FIG. 75 a to aposition diagrammatically depicted in FIG. 75 b. As shown, brake arm1230 is displaced into saw blade 1224 causing the teeth of saw blade1224 to dig into arm 1230 until blade 1224 comes to an immediate stop.

It will be appreciated that cam 1222, cam follower 1226 and brake 1230may comprise alternate geometries without departing from the scope ofthe present invention. Furthermore, cam follower 1226 and brake 1230 mayalternatively be configured to engage another rotating element of thesaw such as the arbor shaft or blade clamp for example.

Referencing now FIGS. 76 a and 76 b, safety mechanism 14 w includingbrake pawls 1232 is shown. Brake pawls 1232 are disposed adjacent sawblade 1234 in a diametrically opposed relationship. Brake pawls 1232 arepivotally coupled to a portion of the saw (not specifically shown) atpivot joints 1236. During a stopping event pawls 1232 are pivotallydisplaced about pivot joints 1236 toward blade 1234.

The operation of safety mechanism 14 w will now be described in greaterdetail. If a dangerous condition is detected by for example one of thesafety mechanisms 12 disclosed herein, brake pawls 1232 are thrust intoblade 1234 from a position diagrammatically depicted in FIG. 76 a to aposition diagrammatically depicted in FIG. 76 b. Preferably, pawls 1232are rotated in a direction opposing rotation of blade 1234. In this way,pawls 1232 rotate counterclockwise into engagement with a clockwiserotating blade 1234. Brake pawls 1232 may be urged into engagement withblade 1234 by for example biasing members, mechanical actuators orexplosive device for example.

Safety Blade

Referencing FIGS. 77 a and 77 b, safety mechanism 14 ww is shown. Safetymechanism 14 ww includes radially actuable guard sections 1250 disposedon saw blade 1252. Guard sections 1250 are configured to rapidlydisplace outwardly beyond the perimeter of blade 1252 during a stopevent. Guard sections 1250 preferably are retained in a position asshown in FIG. 77 a by a latch or similar retaining device (notspecifically shown) during normal operation.

If a dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, guard sections 1250 are urged outwardlyfrom a position as shown in FIG. 77 a to a position as shown in FIG. 77b. Guard sections may be urged by any suitable means such as but notlimited to mechanical biasing members or an explosive device. Guardsections are preferably comprised of a durable pliable materialsufficient to displace a finger or a hand of a user away from the sawblade 1252.

It will be appreciated that alternative configurations of guard sections1250 may be employed. For example an alternate amount of guard sections1250 may be used or alternate geometries may be used for guard sections1250.

External Forces Braking

Another consideration in preventing injury as a result of contact withthe rotating blade of a saw is the size and configuration of the sawblade that is being used. In many applications a standard blade is usedto make cuts through an entire piece of wood. However, additional typesof circular saw blades are available to perform numerous other removalfunctions such as dado operations. These blades and conventional bladesare often made in varying sizes, which may not function correctly withpresently installed stop devices. Therefore, the present inventionprovides a device that allows a user to position a saw brake mechanismin a desired position depending on the size of the saw blade being used.

FIGS. 78 a-78 c show a safety mechanism 14 xx employing brake module1270. Brake module 1270 extends from arbor bracket 1272 and includesactuation fork 1274 attached thereto. Arbor bracket 1272 rotatablycouples saw blade 1276 at shaft 1278. Brake module 1270 which isconnected to arbor bracket 1272 through a pin 1282 in a slot 1286,engages the periphery of blade 1276 to rapidly slow it down during astop event. If a large blade is used (referred to as 1276′ in FIG. 78c), the pin 1282 in the slot 1286 is actuated by the actuation fork 1274to the end of slot 1286 that is further away from the blade 1276 (FIG.78 c). If a smaller blade is going to be used (referred to as 1276 inFIG. 78 b) the pin 1282 in the slot 1286 is actuated by the actuationfork 1274 to the end of slot 1286 that is nearest to the blade 1276(FIG. 78 b).

During a stopping event, brake module 1270 is rotated by suitable meanstoward rotating saw blade 1276. In this way, arbor bracket 1272 maypivot about shaft 1278 clockwise as viewed from FIG. 78 b.Alternatively, brake module 1270 may rotate about shaft 1282 in acounterclockwise direction toward rotating saw blade 1276 as viewed fromFIG. 78 b.

While the following description is provided with reference to a tablesaw, it is readily understood that the contact detection system of thepresent invention is applicable to a variety of power tools and/orwoodworking tools, including (but not limited to) miter saws, radial armsaws, circular saws, band saws, joiners, planars, nailers, drills, etc.

Woodworking power tools of the type described herein are typicallypowered by an electrical power system for connection to a commonlyavailable electrical connection. Therefore the safety devices of thepresent invention are illustrated for use with power tools having apower source that utilizes electrical energy. However, it iscontemplated that the woodworking power tools utilizing a differentpower source may also employ the safety systems described herein and notdepart from the scope of the present invention.

FIG. 79 illustrates a safety mechanism 14 yy for use with a table saw 10yy, box guard 1300. Box guard 1300 is generally compressed of a rivingknife 1302 that is substantially similar in width to saw blade 1304.Riving knife 1302 is oriented coplanar with saw blade 1304 andpositioned directly behind slot 1306. Riving knife 1302 preferablyextends perpendicularly upward with respect to planar top surface 1308to a height that is generally above saw blade 1304. Attached to the topof riving knife 1302 is a plate 1310. Plate 1310 is substantiallyrectangular in shape, having a width that is substantially wider thansaw blade 1304 and a length that extends over the top portion of sawblade 1304. Plate 1310 is connected to a box 1312, which covers sawblade 1304.

In a preferred embodiment, box 1312 is constructed in a box shape havingtwo adjacent sides removed. The first removed side is positionedadjacent to the planar top surface 1308 to allow saw blade 1304 to behoused therein. The second removed side is positioned adjacent to theback of saw blade 1304, near plate 1310 and riving knife 1302. Box 1312is attached to plate 1310 by removable fasteners such as, bolts or pullpins, to form a hinge mechanism that allows box 1312 to be selectivelyraised to allow access to saw blade 1304. Box 1312 may include a rampshaped guide portion 1318 formed on the front edge of the box 1312 toactuate box 1312 when in contact with a piece of material.Alternatively, a knob 1320 or actuator may be utilized to actuate box1312 to an open position. Additionally, a set of louvers 1324 isprovided to allow monitoring of the blade 1304 while limiting the sizeand number of objects that may contact saw blade 1304.

FIG. 80 shows safety mechanism 14 zz according to another embodiment ofthe present invention. Safety mechanism 14 zz includes guard plateassembly 1350 including a riving knife 1352 mounted to table saw 10 zzas known in the art for guiding a workpiece. Releasably attached to thedistal end of riving knife 1352 is a guard plate 1354 that extends oversaw blade 1386 to operatively prevent inadvertent contact with saw blade1386. As shown guard plate 1354 includes a groove 1356 extending alongthe rear portion of guard plate 1354 to receive the top edge of rivingknife 1352. Extending over groove 1356 is a yoke 1360 that retains thefront end of riving knife 1352. Located at the rear of guard plate 1354is manually rotatable latch 1362 to releasably attach guard plate 1354to the rear end of riving knife 1352. If the use of guard plate 1354 isdesired, the front end of riving knife 1352 is inserted into yoke 1360and latch 1362 is actuated to engage the rear portion of riving knife1352. In this configuration, guard plate 1354 provides a protectivemember that extends over the length of saw blade 1386. If the use ofguard plate 1354 is not desired, guard plate 1354 may be removed byrotating latch 1362 to a disengaged position and sliding guard plate1354 forward so that yoke 1360 is not in contact with the leading edgeof riving knife 1352.

As shown in FIG. 81, a safety mechanism 14 ba is shown to include asight guard 1380. Like components of safety mechanism 14 zz are used todesignate like components of safety mechanism 14 ba. Sight guard 1380 isgenerally composed of a rectangular translating guard 1382 having aplurality of louvers 1384 disposed therethrough for observing the sawblade 1356. Translating guard 1382 extends through a simple slot 1390 inguard frame 1392 substantially similar in size to translating guard1382. Sight guard 1380 is selectively positioned in an infinite numberof positions ranging from fully closed, wherein the leading end oftranslating guard 1382 is adjacent to planar top surface 1394, to fullyopen, wherein the leading end of translating guard 1382 is adjacent toguard frame 1392. In operation, translating guard 1382 is actuatedupward until the leading end is above the top surface of a workpiece(not shown). As the workpiece is moved toward the blade 1396, theleading edge of translating guard 1382 follows along the top surface ofthe workpiece. In this configuration, sight guard 1380 allows the userto view the interaction between the saw blade 1396 and the workpiecewhile prevented from contacting saw blade 1396.

FIG. 82 shows safety mechanism 14 ba′ incorporating a plurality rollingmembers 1410 that follow along the inner and outer surface of guard 1380to promote smooth translation of guard 1380. Like reference numbers ofsafety mechanism 14 ba are used to designate like components of safetymechanism 14 ba′. In this regard, the operation of safety mechanism 14ba′ is substantially similar to safety mechanism 14 ba.

FIG. 83 shows safety mechanism 14 bb having sensing guard assembly 1420.Sensing guard assembly 1420 is generally comprised of a riving knife1422 and a top plate 1424 mounted to a table saw as known in the art. Asight guard 1430 is rotatably attached to the front end of the top plate1424, a sensing device 1432 is attached to the front end of sight guard1430 and an actuation mechanism 1436 including motor or solenoid 1434for selectively actuating the sight guard 1430. Sight guard 1430 ispreferably formed to have a plurality of louvers 1440 to allow the userto inspect the interaction between the saw blade 1444 and the workpiecewhile precluding user interface with the saw blade 1444. Connected tothe front of sight guard 1430 is sensor device 1432 oriented to detectin the downward direction. If sensor device 1432 detects a workpiece, itsends a signal to an actuation mechanism 1436 to open sight guard 1430.Actuation mechanism 1436 opens sight guard 1430 to allow a workpiece toaccess saw blade 1444. The downward orientation of sensor device 1432prevents objects such as an operator's finger from contacting saw blade1444 because the blade 1444 must be actuated upward by the person toallow for entrance with the blade 1444. Therefore, the operator wouldknow that they were approaching the saw blade 1444. Alternatively, asensing device that detects the difference between human tissue and aworkpiece as is discussed herein may be installed to further preventinadvertent contact with the saw blade 1444.

As shown in FIG. 84 a safety mechanism 14 bc including a riving knifeassembly 1450 is shown. In operation of a table saw, it may be desiredto utilize a riving knife 1452 to guide a workpiece while performinggroove, finger joint, rabbit, or cheek cuts. However, riving knives arenot able to be used to many other types of cuts. Safety mechanism 14 bcallows for easy installation when using riving knife 1452 and easyremoval when not using riving knife 1452. In a preferred embodiment,riving knife assembly 1450 includes a base member 1456 having a slot1460 therein oriented coplanar and behind a saw blade (not specificallyshown). Base member 1456 includes a pull pin 1464 mounted along anelongated side for selectively engaging a riving knife 1452 having aretention hole 1466 formed complementary to pull pin 1464.

If the use of riving knife 1452 is desired, the operator may slide theriving knife 1425 into the base member 1456 and actuate pull pin 1464away from base member 1456 to install riving knife 1452. Once rivingknife 1452 is fully seated, the operator may return pull pin 1464 to theoriginal position to lock riving knife 1452 to base member 1456. If theuse of riving knife 1452 is not desired, the operator actuates pull pin1464 away from base member 1456 to extract riving knife 1452 from basemember 1456.

With reference to FIG. 85, a safety mechanism 14 bd including guardretainer 1480 is shown. Guard retainer 1480 is configured to lock theblade guard 1450 to pivot plate 1452 and thus allow access to arbor bolt1454. A screw 1460 maintains the guard and pivot plate 1452 in theposition shown. During operation, lower guard 1450 is rotated upward ina counterclockwise direction. Screw 1460 is loosened to clear tab 1462on pivot plate 1452. Concurrently, retainer 1466 biases guard 1450counterclockwise thereby holding the guard 1450 in a retained position.Guard 1450 and pivot plate 1452 are further rotated together until pivotplate tab 1462 moves beyond screw 1460. Screw head 1460 then precludesblade guard 1450 and pivot plate 1452 from rotating clockwise. In thisway, the user may gain unimpeded access to arbor bolt 1454 during ablade change.

Turning now to FIG. 86, a safety mechanism 14 be includingmagneto-rheological damper 1470 is shown operatively associated with amiter saw 10 be. Safety mechanism 14 be is preferably used inconjunction with another safety mechanism 14 disclosed herein. If asensing mechanism 12 initiates a stop event by using a braking forcesuch as those described in association with other safety mechanisms 12.During a stopping event, the rapid deceleration will tend to cause theblade 1472 and arm 1474 to travel downward in the direction of workpiece1478 and also toward potential additional contact with a user. Tocounter this, magneto-rheological damper 1470 precludes downward travelof blade 1472 and arm 1474. As is well known, a magneto-rheologicalfluid damper utilizes a fluid which can have the viscosity alteredthrough the application of a magnetic field. During a stop event, asignal is preferably sent to damper 1470 at the same time a sensingmechanism 12 senses a dangerous condition.

FIGS. 87 and 88 show a safety mechanism 14 bf for use with a power tablesaw 10 bf including blade retraction system 1500. Blade retractionsystem 1500 is designed to retract a saw blade 1502 under the tableportion 1504 of a table saw 10 bf to prevent or reduce injurious contactbetween the saw blade 1502 and an operator of the table saw 10 bf.Again, although the present invention is shown in combination with apower table saw 10 bf, it is appreciated that the teachings of thepresent invention may be applied to other types of power saws having arotating saw blade, such as a miter saw, chop saw, or circular saw.

The blade retraction system 1500 is comprised of an arbor bracket 1508supporting the saw blade 1502 and coupled to a portion of the table saw10 bf, a sector gear 1510 adapted to travel along a portion of the arborbracket 1508, a clutch mechanism 1514 slidably coupling the sector gear1510 to the arbor bracket 1508, a worm gear 1520 operable to adjust theposition of the sector gear 1510 and an actuating device 1526 coupled tothe sector gear 1510 and the arbor bracket operable to translate thearbor bracket 1508 relative to the sector gear 1510 to retract the sawblade 1502 beneath the table portion 1504 of the table saw 1504 toprevent injurious contact between the saw blade 1502 and the operator ofthe table saw 10 bf.

The arbor bracket 1508 of the present invention is shown to be comprisedof a support arm 1529 and an adjustment arm 1530 defined by a bore 1532.The support arm 1526 of the arbor bracket 1508 extends generallyhorizontal and includes a bore adapted to receive a spindle 1536. Thespindle 1536 is adapted to be coupled to the saw blade 1502 and allowrotation of the saw blade 1502 relative to the arbor bracket 1508. Thespindle 1536 also engages a belt or other device (not shown) thatdrivingly engages the saw blade 1502 to operatively rotate the saw blade1502. The adjustment arm 1530 of the arbor bracket 1508 generallyinclude an arc shaped surface 1540 that is substantially concentric withthe bore 1532. The bore 1532 is adapted to engage a pivot pin 1542 thatis coupled to a portion of the table saw 10 bf to allow arbor bracket1508 to rotate relative to the table saw 10 bf.

The sector gear 1510 is formed to have a generally arcuate shape havinga first surface 1552 substantially conforming to the arc shaped surface1540 of the arbor bracket 1508 and a gearing portion 1554 also formed inan arcuate shape substantially concentric to the bore 1532 and having aplurality of gear teeth 1560. The sector gear 1510 is located to allowthe first side of the sector gear 1510 to be adjacent to the arc shapedsurface 1540 of the arbor bracket 1508 to allow relative translationtherebetween.

The clutch mechanism 1514 is designed to couple the arbor bracket 1508to the sector gear 1510, but allow relative translation therebetweenwhen a requisite force is applied to either the arbor bracket 1508 orthe sector gear 1510. The clutch mechanism 1514 is shown to include abiased detent mechanism 1566 extending from the arbor bracket 1508 andengaging the sector gear 1510. The detent mechanism 1566 is comprised ofa detent member 1568 that is biased toward the sector gear 1510 by abiasing member 1570. The detent member 1568 engages the first surface1572 of the sector gear 1510 to prevent translation between the sectorgear 1510 and the arbor bracket 1508. It is contemplated that the othertype of clutch mechanisms 1514, may be used to couple the arbor bracket1508 to the sector gear 1510. Additionally, it is appreciated that theclutch mechanism 1514 may be attached to various locations on the sectorgear 1510.

The worm gear 1520 is adapted to engage the sector gear 1510 to controlmovement of the sector gear 1510. The worm gear 1520 is generallycomprised of a shaft member 1580 and a threaded gear portion 1852. Theworm gear 1520 may to be rotated in one of a number of ways such aselectric actuator or crank. The threaded gear portion 1582 of the wormgear 1520 is adapted to engage some of the plurality of teeth 1560 ofthe sector gear 1520. As the worm gear 1520 is rotated, the threadedgear portion 1582 meshes with the gear teeth 1560, thereby cause thearbor bracket 1508 and attached components to rotate clockwise orcounterclockwise depending on the direction of rotation of the worm gear1520. In operation, the worm gear 1520 is utilized to control the heightof the saw blade 1502 relative to the top of the table portion 1504 ofthe table saw 10 bf.

In a first embodiment, the actuating device 1526 is shown to berotatably coupled to the sector gear 1510 and the arbor bracket 1508.The actuating device 1526 is comprised of a piston 1584 and a cylinder1586. The piston 1586 is coupled to one of the sector gear 1510 and thearbor bracket 1508. The cylinder 1586 is coupled to the other of thesector gear 1510 and the arbor bracket 1508. The actuating device 1526also includes a propellant material disposed in the cylinder 1586 andoperable to expand upon the activation of a triggering device (notshown). Upon activation of the triggering device (not shown), the piston1586 portion of the actuating device 1526 expands axially outwardincreasing the length of the actuating device 1526. The propellantmaterial is preferably an electrically activated explosive material.However, it is contemplated that other types of propellant materials maybe utilized in the present invention. It is also contemplated that amechanical device may be utilized in the place of actuating device 1526.

In operation, the triggering device (not shown) is activated causing theactuating device 1526 to expand axially. As the actuating device 1526expands, the arbor bracket 1508 and the sector gear 1510 are drivenapart. As the actuating device 1526 expands, the arbor bracket 1508 isdriven in a counterclockwise direction. As the arbor bracket 1508rotates, the support arm 1526 and the saw blade 1502 are rotateddownward to a position under the table portion 1504 of the table saw 10bf. Once the saw blade 1502 is beneath the table portion 1504 of thetable saw 10 bf, the possibility of contact between the saw blade 1502and the operator is eliminated.

As shown in FIG. 88, a bumper pad 1590 may be incorporated into theblade retraction system 1500 of safety mechanism 14 bf of the presentinvention. It is appreciated that like reference numbers will be used todesignate like components. The bumper pad 1590 is positioned rearward ofthe arbor bracket 1508 and is adapted to receive the rear end of thearbor bracket 1508 after activation of the actuating device 1526. Thebumper pad 1590 dissipates the energy of the impacting arbor bracket1508. The bumper pad 1590 is shown to be formed of a permanentlydeforming material such as a yielding plastic, a crushing foam or adeformable honeycomb structure. It is also contemplated that the bumperpad 1590 may be constructed of a dampening material such as anengineering foam, or a high friction engagement material such aselastomers.

FIG. 89 illustrates a safety mechanism 14 bg employing an alternateactuation mechanism 1526′. The basic structure of the blade retractionsystem 1500″ is substantially similar to the previous embodimentdescribed above. However, the actuating device 1526′ is different. Theactuating device 1526′ includes a cylinder 1592 that is integrallyformed in the arbor bracket 1508. A piston 1594 is adapted to engage theintegral cylinder 1592. A first end 1596 of the piston 1594 is formed ina frustum spherical shape to allow the piston 1594 to maintainengagement with the inner walls of the cylinder 1592. The other end ofthe piston 1594 is rotatably coupled to the sector gear 1510.Additionally, it is contemplated that a piston having a compliantsealing cap engaging the inner walls of the cylinder may be used. Thepiston/cylinder arrangement operates substantially similar to thepropellant actuated device 1526 described above. It is also contemplatedthat a mechanical device may be utilized in the place of actuatingdevice 1526′.

FIG. 90 illustrates safety mechanism 14 bh. In this embodiment, anactuation device 1526″ is coupled to the arbor bracket 1529′ and aportion of the frame of the table saw 10 bh. The actuation device iscomprised of a piston 1608 and cylinder 1610 substantially similar tothe piston/cylinder arrangement of the actuation device 1526′. Thealternate positioning of the piston 1608 and cylinder 1610 arrangementoperates in substantially similar to the actuation device disclosedabove.

Referring to FIG. 91, a safety mechanism 14 bi for a power tool 10 bihaving a circularly rotating blade 1650 is shown diagrammatically. Thepower tool 10 bi is generally comprised of an arm 1652 rotatably coupledto a rigid base 1654 and having a power saw 1656 attached to the distalend of the arm 1652. The safety mechanism 14 bi includes a brakingdevice 1660 coupled to the base 1654 and to the arm 1652 operable toengage the saw blade 1650 of the power saw 1656. The safety mechanism 14bi of the present invention is shown for use with a miter saw. It iscontemplated that the present invention may be utilized with other typesof power tools having a circular blade. For example, the safetymechanism 14 bi of the present invention may be adapted for use with aradial arm saw, a table saw or a chop saw.

The base member 1654 of tool may be formed as an “L”-shaped memberhaving a first and a second portions 1662 and 1664 that aresubstantially perpendicular. The outwardly extending first portion 1662generally supports the safety mechanism 14 bi and includes a firstconnection 1670 to rotatably couple a portion of the braking device 1660to the base member 1654 to provide proper operation of the brakingdevice 1660. The upwardly extending second portion 1664 includes asecond connection 1672 to rotatably couple an end of the arm 1652 to thebase member 1654 to allow articulation of the power saw 10 bi coupled tothe other end of the arm 1652. However, it is understood that the basemember 1654 may be constructed in a variety of different configurationsthat allow for proper function of the arm 1652 and the braking device1660.

The arm 1652 of the safety mechanism 14 bi is generally formed in an“L”-shape having a first extending end 1676 and a second extending end1678. The first extending end 1676 is rotatably coupled to the basemember 1654 and the second upwardly extending and 1678 is adapted tolocate the power saw 1656 and specifically the axis of rotation 1680above the first extending end 1676. The arm 1652 also includes a brakeconnection 1682 for coupling a brake device thereto. The brakeconnection 1682 is located proximate to the saw blade 1650 of the powertool 10 bi. The arm 1652 is designed to allow proper articulation of thesaw blade 1650 with respect to a workpiece (not shown). The arm 1652 isshown to be formed of a rigid material having a relatively high strengthsuch as steel. However, it is contemplated that the arm 1652 may beconstructed of other material having suitable properties.

The power saw 1656 is attached to the distal end of the arm 1652. Thearm 1652 allows the power saw 1656 to be articulated along a pathdefined by the distal end of the arm 1652. The power saw 1656operatively rotates the saw blade 1650 in the clockwise directionindicated by arrow 1688.

The power saw 1656 portion of the present invention is shown to beconstructed of a AC electric motor coupled to a saw blade 1650 by anarbor. However it is contemplated that many different varieties of powersaws, such as DC electric and saws having a hydrocarbon based engine,may be used with the safety mechanism 14 bi of the present invention.

The braking device 1660 includes a brake 1690, coupled to the arm 1652and operable to engage the saw blade 1650 upon translation of anactivation mechanism 1692. The activation mechanism 1692 is operable tobe activated on the occurrence of a predetermined event, such as asignaling by the operator, jammed workpiece, or detection of a dangerouscondition by a sensing mechanism 12 as disclosed herein.

The activation mechanism 1692 is generally comprised of a piston 1696coupled to the brake connection 1682 of the arm 1652 and a cylinder 1698having an explosive material 1700 disposed therein and coupled to thebase 1654. The explosive material 1700 disposed in the cylinder 1698 maybe activated in any number of ways known to activate explosives 1700such as temperature or spark.

In a first preferred embodiment the brake 1690 is formed to have a link1706 rotatably coupled to the arm 1652. The link is generally comprisedof a connection arm 1710 and a push arm 1712. The connection arm 1710 isrotatably coupled to the distal end of the piston 1696. The push arm1712 is located proximate to the edge of the saw blade 1650 and includesa brake pad 1718 adapted to engage the saw blade 1650.

Upon activation of the activation portion, the connection arm 1710 ofthe link 1706 is driven upward rapidly from the force of the explosives1700. The use of explosives 1700 is preferred over many other commonlyknown biasing devices because explosives 1700 provide a large force veryrapidly. This large and rapid force allows the saw blade 1650 of thepower saw 10 bi to be stopped in a short period of time, therebyreducing the chance of serious injury from contact with the saw blade1650. As the connection arm 1710 of the link 1706 is driven upward, thepad 1718 located on the push end of the link 1706 is driven intoengagement with the edge of the saw blade 1650. The saw blade 1650 israpidly slowed as the teeth of the saw blade 1650 engage the pad 1718until the saw blade 1650 is stopped.

Additionally, the relative location of the pad 1718, above the axis ofrotation 1680 of the saw blade 1650 causes the rotational inertia of thesaw blade 1650 to be dissipated in the upward direction, thus moving thesaw blade 1650 and power saw 1656 away from the operator.

A second embodiment of a brake is shown in FIG. 93. The brake 1720 issimilar to the brake 1690, and thus only portions of brake 1720 that aredifferent will be discussed. The push arm 1722 of link 1706 is adaptedto engage a first and a second pivoting break members 1728 and 1730. Thebrake members 1734 and 1736 are adapted to engage the edge of the sawblade 1650. The first and the second brake members 1728 and 1730 includea first and second cam surfaces 1740 and 1742 that engage a first andsecond edges 1744 and 1746 of the push arm 1722. As the first and secondbrake members 1734 and 1736 are activated to a first and second brakepads 1734 and 1736 engage the edge of the saw blade 1650.

A third embodiment of a brake is shown in FIG. 94. The brake 1750includes a wedge or panel brake 1752 adapted to engage the saw blade1650. Upon activation of the brake 1750, push arm 1722 forces wedge 1752into blade 1650. As wedge 1752 engages the saw blade 1650, the wedge1752 engages the teeth of blade 1650. The wedge shape of wedge 1752causes it to be drawn into further engagement with the saw blade 1650,until the saw blade 1650 is stopped.

While the invention has been described in its presently preferred form,it will be understood that the invention is capable of modificationwithout departing from the spirit of the invention as set forth in theappended claims.

What is claimed is:
 1. A power tool, comprising: an active portiondriven by a motor; a pawl disposed proximate to the active portion andpivotally coupled at a first end to a frame member of the power tool; abiasing member engaged with the pawl and operating to urge the pawl intoengagement with the active portion; a release mechanism selectivelycoupled between the pawl and the frame member, wherein the pawl isdisengaged from the active portion when the release mechanism is coupledto the pawl and the pawl is biased by the biasing member into engagementwith the active portion when the release member is uncoupled from thepawl; a transmitter capacitively coupled to the active portion andoperable to transmit an electrical signal to the active portion; areceiver capacitively coupled to the active portion and operable toreceive the electrical signal transmitted to the active portion; acontroller connected to the receiver and the release mechanism, thecontroller operable to detect a variation in the electrical signal andsend an activation signal to the release mechanism when the variation inthe electrical signal exceeds a threshold value, where the releasemechanism uncouples the pawl in response to the activation signals andthe controller adjusts the threshold value in accordance with parasiticcapacitance present at the active portion during motion of the activeportion.
 2. The power tool of claim 1 wherein the biasing member isfurther defined as a spring.
 3. The power tool of claim 1 wherein therelease mechanism is further defined as a fuse.
 4. The power tool ofclaim 1 wherein release mechanism includes a wire coupled at one end tothe pawl and the other end to the frame member.
 5. The power tool ofclaim 1 wherein the controller adjusts the threshold value in accordancewith a drive signal of the transmitter.
 6. The power tool of claim 5wherein the controller increases the threshold value when the parasiticcapacitance increases.
 7. The power tool of claim 5 wherein thecontroller decreases the threshold value when the parasitic capacitancedecreases.
 8. A power tool, comprising: a frame structure; a blademounted on a spindle that is supported by the frame structure; a drivemotor mounted to the frame structure and configured to drive thespindle; a pawl disposed proximate to the blade and pivotally coupled ata first end to a frame structure; a biasing member engaged with the pawland operating to urge the pawl into engagement with the blade; a releasemechanism selectively coupled between the pawl and the frame structure,the pawl being disengaged from the blade when the release mechanism iscoupled to the pawl and the pawl is biased by the biasing member intoengagement with the blade when the release member is uncoupled from thepawl; a transmitter capacitively coupled to the blade and operable totransmit an electrical signal to the blade; a receiver capacitivelycoupled to the blade and operable to receive the electrical signaltransmitted to the blade; a controller connected to the receiver and therelease mechanism, the controller operable to detect a variation in theelectrical signal and send an activation signal to the release mechanismwhen the variation in the electrical signal exceeds a threshold value,where the release mechanism uncouples from the pawl in response to theactivation signals and the controller adjusts the threshold valueaccording to parasitic capacitance present at the blade while the bladeis being driven.
 9. The power tool of claim 8 wherein the releasemechanism is further defined as a fuse.
 10. The power tool of claim 8wherein release mechanism includes a wire coupled at one end to the pawland the other end to the frame structure.
 11. The power tool of claim 8wherein release mechanism includes a wire arranged in a loop around aportion of the pawl, the wire having a first end and a second endcoupled to the frame structure.
 12. The power tool of claim 8 whereinthe controller adjusts a magnitude of the electrical signal transmittedby the transmitter in order to maintain signal strength of theelectrical signal received by the receiver and adjusts the thresholdvalue in accordance with the magnitude of the electrical signaltransmitted by the transmitter.
 13. The power tool of claim 12 whereinthe controller increases the threshold value when the parasiticcapacitance increases.
 14. The power tool of claim 12 wherein thecontroller decreases the threshold value when the parasitic capacitancedecreases.
 15. A table saw comprising: a frame structure with agenerally flat work surface; a blade mounted on a spindle and beingadapted to have at least a portion of the blade extending above the worksurface; a drive motor mounted to the frame structure and configured todrive the spindle; a pawl disposed proximate to the blade; a biasingmember engaged with the pawl and operating to urge the pawl intoengagement with the blade; a release mechanism selectively coupledbetween the pawl and the frame structure, the pawl being disengaged fromthe blade when the release mechanism is coupled to the pawl and the pawlis biased by the biasing member into engagement with the blade when therelease member is uncoupled from the pawl; a transmitter capacitivelycoupled to the blade and operable to transmit an electrical signal tothe blade; a receiver capacitively coupled to the blade and operable toreceive said electrical signal transmitted to the blade; and acontroller connected to said receiver, said controller operable todetect a variation in said electrical signal and send an activationsignal to a braking mechanism when said variation in said electricalsignal exceeds a threshold value, where the release mechanism uncouplesfrom the pawl in response to the activation signals and said controlleradjusts said threshold value according to parasitic capacitance presentat the blade while the blade is being driven.
 16. The power tool ofclaim 15 wherein the release mechanism is further defined as a fuse. 17.The power tool of claim 15 wherein release mechanism includes a wirecoupled at one end to the pawl and the other end to the frame structure.18. The power tool of claim 15 wherein release mechanism includes a wirearranged in a loop around a portion of the pawl, the wire having a firstend and a second end coupled to the frame structure.
 19. The power toolof claim 15 wherein the controller adjusts a magnitude of the electricalsignal transmitted by the transmitter in order to maintain signalstrength of the electrical signal received by the receiver and adjuststhe threshold value in accordance with the magnitude of the electricalsignal transmitted by the transmitter.
 20. The power tool of claim 19wherein the controller increases the threshold value when the parasiticcapacitance increases.
 21. The power tool of claim 19 wherein thecontroller decreases the threshold value when the parasitic capacitancedecreases.